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Jesse Ramsden

Jesse Ramsden made optical instruments like telescopes, theodolites and sextants during the middle of the 18th century. One such instrument, was a sextant much prized by Captain Cook in his voyages of discovery in the Great Southern Oceans (http://www.captaincooksociety.com/ccsu4119.htm). This same Ramsden made another sextant which was used by Captain Philip on the first fleet voyage from England to Botany Bay in 1788. So it can be said that a Ramsden assisted in the discovery AND colonization of Australia and New Zealand, and the discovery and mapping of the other islands of the Pacific (including Hawaii). Furthermore, the famous (to Australians) New South Wales (NSW) explorer Lieutenant John Oxley as Surveyor General of the (colonial) Territory (of NSW) relied upon a Ramsden made theodolite for his surveying in his journeys of exploration of the NSW interior during 1817–18. At that time, NSW occupied all of the land now known as the Australian states of New South Wales, Northern Territory, Queensland, South Australia and Victoria. Only Western Australia had been annexed from New Holland (as mainland Australia was known then) by English decree conveniently sliced down the ?? latitude on a map. Australia occupied a similar land mass as Western Europe, however, to those in England, the carving up of a distant unexplored (and unknown) English colonial kingdom was as easy as ruling a vertical or horizontal line on a map of the time. So it can also be said that this Ramsden assisted in the size and position of the Australian States, as this required an appropriate latitude and longitude measurement to position the state borders, which was provided by his optical mathematical instruments. Apparently, the Ramsden disk is the name given to the small disk of light visible in the back focal plane of an eyepiece. And that there's a Ramsden lens for use in telescopes, comprised of a 2-piece field lens and eye lens. Did you know that there is a 24Km wide feature on the Earth's moon named the 'Ramsden Crater'? In fact, Jesse Ramsden was also responsible for the 'Ramsden lens' used in telescopes, and this crater on the moon was posthumously named after him. Some wit has created a tongue-in-cheek website which claims that an observatory on the dark side of the moon is named the 'Ramsden Observatory' in honour of Jesse's achievements. In the third moon picture, Rimae Ramsden is the spiderweb set of narrow depression lines on the right side of the photo, with crater Ramsden to their right. (As taken by Carol Lakomiak on Sun Dec 14 02:02:02 2003 UTC and displayed at Solar Terrestrial Dispatch http://www.spacew.com/gallery/image002415.html) Jesse's theodolite was used measuring the angles in the Primary Triangulation of Great Britain. This was the first accurate survey of Britain and formed the foundation for the Ordnance Survey maps of the country. The huge project was initiated by General William Roy, who had advocated a national survey since 1763. The government at first declined, on grounds of cost, but the impetus to start finally came from a French request to the Royal Society to collaborate and measure the relative positions of the London and Paris observatories. The enterprise appealed to the scientific spirit of George III who helped to fund the work. This initial project subsequently grew into the national Ordnance Survey of Britain in 1787. Jesse Ramsden was one of the foremost instrument-makers of his age. Two Ramsden theodolites were used in the survey and the first could take a bearing on a mark 70 miles away with an error of only 1/180th of a degree. The theodolite shown here is the second instrument, which was still more accurate. Despite their great weight, the theodolites were carried to the tops of mountains, steeples and specially-built scaffolds to obtain lines of sight. The measurements taken during the survey were so accurate that they were used for the next 150 years. According to (http://www.makingthemodernworld.org.uk/stories /enlightenment_and_measurement/05.ST.05/?scene=3) In the last decade of the eighteenth century the Royal Society set up a series of experiments to determine the best method of finding the alcohol content of liquids using a very accurate balance by the instrument maker Jesse Ramsden. According to the British Society for the History of Mathematics (at http://www.dcs.warwick.ac.uk/bshm/zingaz/ LondonPeopleN.html#rams) Jesse Ramsden (1735-1800) came to London as an apprentice to Burton, a mathematical instrument maker, in 1758. Set up on his own in 1762. Married Sarah Dollond, daughter of John Dollond in 1765 (or 1766). Inventor of circular dividing engines. The first to use vernier scales on circular instruments. For the triangulation of southeast England, Ramsden designed and built the cased glass tubing and a coffered steel chain, used for two of the three measurements of the base line in 1784. He also designed and built a new theodolite, 3 ft in diameter and weighing 200 lbs. This was completed in 1787 and the triangulation was completed in 1789. It could read a mark 70 miles away with an error of only 2 seconds. It continued in use until 1853, and then was stored in the Ordnance Survey's Office in Southampton, where it was destroyed in WW2. FRS, 1786. However, Ramsden was such a perfectionist that most of instruments were delayed. Roy was so annoyed that the drafts of his reports contain many derogatory references to Ramsden which were deleted from the published forms. George III once remarked that Ramsden appeared at Buckingham Palace at the appointed day and hour, but a year late! [Yolande O'Donoghue, William Roy 1726-1790 Pioneer of the Ordnance Survey, British Library, 1977.] According to their entry for William Roy (http://www.dcs.warwick.ac.uk/bshm/zingaz/ LondonPeopleN.html#roy), Starting on 16 Apr 1784 and continuing through the summer, a length of 27,404.72 feet was set out and measured three times - using cased glass tubing made by Ramsden, seasoned deal rods and a coffered steel chain made by Ramsden. The glass tubing was considered to be the most accurate, but the three measurements agreed to within three inches and the steel rods were later adopted as standard. Roy published this in the Phil. Trans. of the RS in 1785 and was awarded the RS Copley Medal on 30 Nov 1785. Roy realised that all the surveying instruments needed to be thoroughly redesigned to obtain the desired precision. In particular, Ramsden designed and built a new theodolite, 3 ft in diameter and weighing 200 lbs. This was completed in 1787 and the triangulation was completed in 1789. In 1787, the survey had reached the coast and a line was measured on Romney Marsh using Ramsden's steel chain and the measured length agreed with the calculated length to within a foot. [Yolande O'Donoghue, William Roy 1726-1790 Pioneer of the Ordnance Survey, British Library, 1977.] According to (http://20.1911encyclopedia.org/E/EA/EARTH.htm) A precision previously unknown was attained by the use of Ramsdens theodolite, which was the first to make the spherical excess of triangles measurable. The wooden rods with which the first base was measured were replaced by glass rods, which were afterwards rejected for the steel chain of Ramsden. A Ramsden 3ft (36") azimuth circle theodolite and Ramsden steel chain were used by the Swiss geodetic surveyor Ferdinand Hassler in the survey of Berne in 1798. See http://www.fig.net/pub/fig_2002/HS2/HS2_glatthard_bollinger.pdf, and at http://www.lib.noaa.gov/edocs/HASSLER1.htm Jesse's Quadrant was used by Spanish Explorers of the era. See http://www.palmbeach.k12.fl.us/Multicultural/Updates/ SpainResource.pdf. When leading instrument makers such as Jesse Ramsden and the Troughtons began to use dividing engines for their scales, smaller and lighter instruments could be produced in large numbers without loss of accuracy. See (http://www.makingthemodernworld.org.uk/stories/ enlightenment_and_measurement/05.ST.05/?scene=8). Eighteenth-century craftsmen marked out the degree scales on scientific instruments with great accuracy, using basic geometrical principles, compasses and hand tools. However, this was a time-consuming task. During this period, navigating accurately at sea was a pressing problem. Dividing engines were devised to produce the octants and sextants which were increasingly used to find the altitude of the Sun or stars. The first circular dividing engine was completed in about 1774 by Jesse Ramsden, earning an award from the Board of Longitude - the body that ultimately rewarded the chronometer pioneer John Harrison. This machine is believed to be a close copy of Ramsden's engine, completed by John Troughton in 1778. Although using a dividing engine was faster than hand-dividing, it was backbreaking work for the operator, who had to lean over the engine. John's brother Edward wrote that, 'it had done no good either to his health or that of my own'. However, it was a profitable business and Troughton became one of London's major instrument makers. See (http://www.makingthemodernworld.org.uk/icons_of_invention/ science/1750-1820/IC.045/). Probably the finest 18th century instrument maker was the Englishman Jesse Ramsden. His specialty was accurate scale division. Here’s a small brass pentant (illustrated) that Ramsden made shortly before his death in 1800. Ramsden's major achievement was to invent a highly accurate "dividing engine"—the apparatus used to divide the scale into degrees and fractions of degrees. His design was considered so ingenious that the British Board of Longitude awarded Ramsden a prize of 615 pounds—in 18th century terms, a small fortune. His "dividing engine" now resides in the Smithsonian Institution in Washington. The development of more precise scale division was a milestone in instrument development. Certainly, it permitted more accurate observations but it also permitted smaller, lighter, more easily handled instruments. See http://www.mat.uc.pt/~helios/Mestre/Novemb00/H61iflan.htm The History of the Sextant by Peter Ifland, Ph. D. in Biochemistry (U. of Texas) Commander in the US Naval Reserve Author of Taking the Stars: Celestial Navigation from Argonauts to Astronauts, The Mariners' Museum, Newport News, Virginia, 1998 and of numerous articles about navigation and navigation instruments Ramsden pentant. To be correct, the instrument should be called a pentant, a fifth of a circle, rather than a sextant. This jewel is only 4 1/2 inches radius. The scale is divided on silver from minus 5 degrees to 155 degrees with each degree further divided in three to 20 arc minutes. As you can see, the scale is beveled at 45 degrees. The Ramsden eyepiece is described at http://www.astro.uvic.ca/astrocourses/a200/a200/node32.html as a two-component eyepiece, consisting of a field lens and an eye lens. The plane surface of the field lens should face the object glass, and the plane surface of the eye lens should face the eye, so that the two convex surfaces are facing each other. Keep looking through the telescope and move the field lens slowly towards you, just enough that the dust, etc., becomes sufficiently out of focus that it is not visible. Do not go any further than this, for you are introducing lateral chromatic aberration the more you move the field lens. Jesse was also involved in manufacturing static electricity generation machines. According to http://www.sparkmuseum.com/FRICTION_HIST.HTM One of the earliest and certainly classic friction machines is the Ramsden machine, as pictured. Construction A large circular plate of glass is mounted vertically on a metal axle, about which it can easily be turned by a crank handle. When passing between the two wooden supports, the surface of the glass is rubbed by two pairs of pads fixed to the supports. The rotation of the glass then causes it to become electrified positively on both faces. The negative charge of the pads is neutralized by being connected to the ground through the frame, which is not insulated. Each pad is stuffed with hair, and is covered with leather: Its surface is coated with mosaic gold, or an amalgam of mercury with zinc, bismuth, or tin. Attached to the pads are silk cases which enclose the glass plate nearly as far as the combs, these are to prevent loss of charge. Once the electrical differential has been produced by the action of the pads on the glass, the charge must be collected in some way. Most friction machines do this via prime‑conductors. They consist of two long brass cylinders terminated at each end by knobs, and insulated by glass legs. These cylinders are connected to one another (at the opposite end from the plate) by a metal rod. The ends of the conductors nearest the machine carry metallic combs bent round and brought with the points close to both faces of the glass plate, but not quite touching it (Franklin's points). Operation When the handle of the machine is turned the glass plate is charged positively by friction against the pads; while in this state it acts by influence (inductance) on the conductors, repelling a positive charge to the ends of the conductors, and leaving the parts nearest to it, the combs, negative. The negative charge sets up an "electric wind" at the points of the combs, producing a continual discharge between the surface of the glass and the prime‑conductors. The glass is continually being re‑electrified positively by friction with the pads, thus causing an accumulation of electricity on the conductor. An electroscope may be placed on one of the conductors in order to show the increase of the charge of the electricity. To insure the proper working of the machine it is always necessary to have the room warm and dry; the glass legs supporting the conductors should be well cleaned before use, and wiped with a warm piece of flannel with a little paraffin oil upon it. References: http://chem.ch.huji.ac.il/~eugeniik/history/ramsden.html Ramsden Eyepiece description http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/eyepiece.html http://www.makingthemodernworld.org.uk/stories/enlightenment_ and_measurement/05.ST.05/?scene=4 http://www.makingthemodernworld.org.uk/people/BG.0100/ For further details and measurements obtained from the triangulation base lines, see http://www.sacred-texts.com/earth/za/za40.htm Biography: Jesse's biography is described at http://microscopy.fsu.edu/optics/timeline/people/ramsden.html and duplicated at http://www-history.mcs.st-andrews.ac.uk/Mathematicians/Ramsden.html , and at http://en.wikipedia.org/wiki/Jesse_Ramsden. October 6, 1735 – November 5, 1800. Born in Salterhebble near Halifax, England [of the Huddersfield, West Yorkshire Ramsdens] After serving his apprenticeship with a cloth-worker in Halifax, he went in 1755 to London, where in 1758 he was apprenticed to a mathematical instrument maker. About four years afterwards he started business on his own account and secured a great reputation with his products. He died at Brighton. Ramsden's speciality was divided circles, which began to supersede the quadrants in observatories towards the end of the 18th century. His most celebrated work was a 5-feet vertical circle, which was finished in 1789 (background image in portrait) and was used by Giuseppe Piazzi at Palermo in constructing his catalogue of stars. He was the first to carry out in practice a method of reading off angles (first suggested in 1768 by the duke of Chaulnes) by measuring the distance of the index from the nearest division. line by means of a micrometer screw which moves one or two fine threads placed in the focus of a microscope. Ramsden's transit instruments were the first which were illuminated through the hollow axis; the idea was suggested to him by Prof. Henry Ussher in Dublin. He published a Description of an Engine for dividing Mathematical Instruments in 1777. Ramsden is also responsible for the achromatic eyepiece named after him, and also worked on new designs of electrostatic generators. He was elected to the Royal Society in 1786. In c.1785 or so, Ramsden provided a new large theodolite for General William Roy, of the Royal Engineers, which was used for a new survey of the distance between Greenwich, London and Paris. This work provided the basis for the subsequent Ordnance Survey of the counties of Britain. For his part with Roy in this work he received the Copley Medal in 1795. Octants and Sextants (http://en.wikipedia.org/wiki/Sextant) A sextant is a measuring instrument used to measure the angle of elevation of a celestial object above the horizon. Making this measurement is known as sighting the object or taking a sight. The angle, and the time when it was measured, are used to calculate a position line on a nautical or aeronautical chart. A common use of the sextant is to sight the sun at noon to find one's latitude. The scale of a sextant has a length of 1/6 of a full circle; 60°, hence the sextant's name. An octant is a similar device with a shorter scale, 1/8 of a circle; 45°, which was in use until 1767 when it was quickly replaced by the sextant. In 1767 the first edition of the nautical almanac tabulated lunar distances, enabling navigators to find the current time from the angle between the sun and the moon. This angle is however sometimes larger than 90°, and thus not possible to measure with an octant. Hold the instrument vertically and point it toward the celestial body. Sight the horizon through an unsilvered portion of the horizon mirror. Adjust the index arm until the image of the sun or star, which has been reflected first by the index mirror and second by the silvered portion of the horizon mirror, appears to rest on the horizon. The altitude of the heavenly body can be read from the scale on the arc of the instrument’s frame. The horizon and celestial object remain steady when viewed through a sextant, even when the user is on a moving ship. This occurs because the sextant views the (unmoving) horizon directly, and views the celestial object through two opposed mirrors that subtract the motion of the sextant from the reflection. A sextant's view merges two views. One view is of the sky, through the mirrors. The other view is of the horizon. One uses a sextant by adjusting the arm and a worm adjustment until the lower edge of an image of a celestial body touches the horizon. The measurement is timed to occur on a time-mark spoken by an assistant with a watch. The angle of elevation is then read from the scale, a vernier and a worm adjustment screw, and recorded with the time. After a sight is taken, it is reduced to a position by following any of several mathematical procedures. The simplest sight reduction is to draw the equal-elevation circle of the sighted celestial object on a globe. The intersection of that circle with a dead reckoning track, or another sighting gives a precise location. Theodolites (http://en.wikipedia.org/wiki/Theodolite) A theodolite (Amer. "transit") is an instrument for measuring both horizontal and vertical angles, as used in triangulation networks. It consists of a telescope mounted movably within two perpendicular axes, the horizontal or trunnion axis, and the vertical axis. These must be mutually perpendicular. The optical axis of the telescope, called sight axis and defined by the optical center of the objective and the center of the cross-hairs in its focal plane, must similarly be perpendicular to the horizontal axis. Both axes of a theodolite are equipped with graduated circles that can be read The history of theodolites goes back to so-called plane table alhidades, devices allowing the graphical mapping of the terrain. These devices consisted of a plane table and a telescope mounted in a fork-like contraption or alhidade, allowing it to be aimed out of the horizontal plane. The whole assembly rested on a plane table, onto which graphing paper was attached; a ruler connected to the alhidade in such a way as to be always pointing in the same horizontal direction as the telescope, was then used to plot the direction to the target. Triangulation, as invented by Gemma Frisius around 1533, consists of making such direction plots of the surrounding landscape from two separate standpoints. After that, the two graphing papers are superimposed, providing a scale model of the landscape, or rather the targets in it. The true scale can be obtained by just measuring one distance both in the real terrain and in the graphical representation.	Images

Jesse Ramsden made optical instruments like telescopes, theodolites and sextants during the middle of the 18th century. One such instrument, was a sextant much prized by Captain Cook in his voyages of discovery in the Great Southern Oceans (http://www.captaincooksociety.com/ccsu4119.htm).

This same Ramsden made another sextant which was used by Captain Philip on the first fleet voyage from England to Botany Bay in 1788. So it can be said that a Ramsden assisted in the discovery AND colonization of Australia and New Zealand, and the discovery and mapping of the other islands of the Pacific (including Hawaii).

Furthermore, the famous (to Australians) New South Wales (NSW) explorer Lieutenant John Oxley as Surveyor General of the (colonial) Territory (of NSW) relied upon a Ramsden made theodolite for his surveying in his journeys of exploration of the NSW interior during 1817–18.

At that time, NSW occupied all of the land now known as the Australian states of New South Wales, Northern Territory, Queensland, South Australia and Victoria. Only Western Australia had been annexed from New Holland (as mainland Australia was known then) by English decree conveniently sliced down the ?? latitude on a map.

Australia occupied a similar land mass as Western Europe, however, to those in England, the carving up of a distant unexplored (and unknown) English colonial kingdom was as easy as ruling a vertical or horizontal line on a map of the time. So it can also be said that this Ramsden assisted in the size and position of the Australian States, as this required an appropriate latitude and longitude measurement to position the state borders, which was provided by his optical mathematical instruments.

Apparently, the Ramsden disk is the name given to the small disk of light visible in the back focal plane of an eyepiece. And that there's a Ramsden lens for use in telescopes, comprised of a 2-piece field lens and eye lens.

Did you know that there is a 24Km wide feature on the Earth's moon named the 'Ramsden Crater'? In fact, Jesse Ramsden was also responsible for the 'Ramsden lens' used in telescopes, and this crater on the moon was posthumously named after him. Some wit has created a tongue-in-cheek website which claims that an observatory on the dark side of the moon is named the 'Ramsden Observatory' in honour of Jesse's achievements.

In the third moon picture, Rimae Ramsden is the spiderweb set of narrow depression lines on the right side of the photo, with crater Ramsden to their right. (As taken by Carol Lakomiak on Sun Dec 14 02:02:02 2003 UTC and displayed at Solar Terrestrial Dispatch http://www.spacew.com/gallery/image002415.html)

Jesse's theodolite was used measuring the angles in the Primary Triangulation of Great Britain. This was the first accurate survey of Britain and formed the foundation for the Ordnance Survey maps of the country.

The huge project was initiated by General William Roy, who had advocated a national survey since 1763. The government at first declined, on grounds of cost, but the impetus to start finally came from a French request to the Royal Society to collaborate and measure the relative positions of the London and Paris observatories. The enterprise appealed to the scientific spirit of George III who helped to fund the work. This initial project subsequently grew into the national Ordnance Survey of Britain in 1787.

Jesse Ramsden was one of the foremost instrument-makers of his age. Two Ramsden theodolites were used in the survey and the first could take a bearing on a mark 70 miles away with an error of only 1/180th of a degree. The theodolite shown here is the second instrument, which was still more accurate. Despite their great weight, the theodolites were carried to the tops of mountains, steeples and specially-built scaffolds to obtain lines of sight. The measurements taken during the survey were so accurate that they were used for the next 150 years.

According to (http://www.makingthemodernworld.org.uk/stories
/enlightenment_and_measurement/05.ST.05/?scene=3) In the last decade of the eighteenth century the Royal Society set up a series of experiments to determine the best method of finding the alcohol content of liquids using a very accurate balance by the instrument maker Jesse Ramsden.

According to the British Society for the History of Mathematics (at http://www.dcs.warwick.ac.uk/bshm/zingaz/
LondonPeopleN.html#rams) Jesse Ramsden (1735-1800) came to London as an apprentice to Burton, a mathematical instrument maker, in 1758. Set up on his own in 1762. Married Sarah Dollond, daughter of John Dollond in 1765 (or 1766). Inventor of circular dividing engines. The first to use vernier scales on circular instruments. For the triangulation of southeast England, Ramsden designed and built the cased glass tubing and a coffered steel chain, used for two of the three measurements of the base line in 1784. He also designed and built a new theodolite, 3 ft in diameter and weighing 200 lbs. This was completed in 1787 and the triangulation was completed in 1789. It could read a mark 70 miles away with an error of only 2 seconds. It continued in use until 1853, and then was stored in the Ordnance Survey's Office in Southampton, where it was destroyed in WW2. FRS, 1786. However, Ramsden was such a perfectionist that most of instruments were delayed. Roy was so annoyed that the drafts of his reports contain many derogatory references to Ramsden which were deleted from the published forms. George III once remarked that Ramsden appeared at Buckingham Palace at the appointed day and hour, but a year late! [Yolande O'Donoghue, William Roy 1726-1790 Pioneer of the Ordnance Survey, British Library, 1977.]

According to their entry for William Roy (http://www.dcs.warwick.ac.uk/bshm/zingaz/
LondonPeopleN.html#roy), Starting on 16 Apr 1784 and continuing through the summer, a length of 27,404.72 feet was set out and measured three times - using cased glass tubing made by Ramsden, seasoned deal rods and a coffered steel chain made by Ramsden. The glass tubing was considered to be the most accurate, but the three measurements agreed to within three inches and the steel rods were later adopted as standard. Roy published this in the Phil. Trans. of the RS in 1785 and was awarded the RS Copley Medal on 30 Nov 1785. Roy realised that all the surveying instruments needed to be thoroughly redesigned to obtain the desired precision. In particular, Ramsden designed and built a new theodolite, 3 ft in diameter and weighing 200 lbs. This was completed in 1787 and the triangulation was completed in 1789. In 1787, the survey had reached the coast and a line was measured on Romney Marsh using Ramsden's steel chain and the measured length agreed with the calculated length to within a foot. [Yolande O'Donoghue, William Roy 1726-1790 Pioneer of the Ordnance Survey, British Library, 1977.]

According to (http://20.1911encyclopedia.org/E/EA/EARTH.htm) A precision previously unknown was attained by the use of Ramsdens theodolite, which was the first to make the spherical excess of triangles measurable. The wooden rods with which the first base was measured were replaced by glass rods, which were afterwards rejected for the steel chain of Ramsden.

A Ramsden 3ft (36") azimuth circle theodolite and Ramsden steel chain were used by the Swiss geodetic surveyor Ferdinand Hassler in the survey of Berne in 1798. See http://www.fig.net/pub/fig_2002/HS2/HS2_glatthard_bollinger.pdf, and at http://www.lib.noaa.gov/edocs/HASSLER1.htm

Jesse's Quadrant was used by Spanish Explorers of the era.
See http://www.palmbeach.k12.fl.us/Multicultural/Updates/
SpainResource.pdf.

When leading instrument makers such as Jesse Ramsden and the Troughtons began to use dividing engines for their scales, smaller and lighter instruments could be produced in large numbers without loss of accuracy. See (http://www.makingthemodernworld.org.uk/stories/
enlightenment_and_measurement/05.ST.05/?scene=8).

Eighteenth-century craftsmen marked out the degree scales on scientific instruments with great accuracy, using basic geometrical principles, compasses and hand tools. However, this was a time-consuming task. During this period, navigating accurately at sea was a pressing problem. Dividing engines were devised to produce the octants and sextants which were increasingly used to find the altitude of the Sun or stars. The first circular dividing engine was completed in about 1774 by Jesse Ramsden, earning an award from the Board of Longitude - the body that ultimately rewarded the chronometer pioneer John Harrison. This machine is believed to be a close copy of Ramsden's engine, completed by John Troughton in 1778. Although using a dividing engine was faster than hand-dividing, it was backbreaking work for the operator, who had to lean over the engine. John's brother Edward wrote that, 'it had done no good either to his health or that of my own'. However, it was a profitable business and Troughton became one of London's major instrument makers. See (http://www.makingthemodernworld.org.uk/icons_of_invention/
science/1750-1820/IC.045/).

Probably the finest 18th century instrument maker was the Englishman Jesse Ramsden. His specialty was accurate scale division. Here’s a small brass pentant (illustrated) that Ramsden made shortly before his death in 1800. Ramsden's major achievement was to invent a highly accurate "dividing engine"—the apparatus used to divide the scale into degrees and fractions of degrees. His design was considered so ingenious that the British Board of Longitude awarded Ramsden a prize of 615 pounds—in 18th century terms, a small fortune. His "dividing engine" now resides in the Smithsonian Institution in Washington. The development of more precise scale division was a milestone in instrument development. Certainly, it permitted more accurate observations but it also permitted smaller, lighter, more easily handled instruments. See http://www.mat.uc.pt/~helios/Mestre/Novemb00/H61iflan.htm The History of the Sextant by Peter Ifland, Ph. D. in Biochemistry (U. of Texas) Commander in the US Naval Reserve Author of Taking the Stars: Celestial Navigation from Argonauts to Astronauts, The Mariners' Museum, Newport News, Virginia, 1998 and of numerous articles about navigation and navigation instruments

Ramsden pentant. To be correct, the instrument should be called a pentant, a fifth of a circle, rather than a sextant. This jewel is only 4 1/2 inches radius. The scale is divided on silver from minus 5 degrees to 155 degrees with each degree further divided in three to 20 arc minutes. As you can see, the scale is beveled at 45 degrees.

The Ramsden eyepiece is described at http://www.astro.uvic.ca/astrocourses/a200/a200/node32.html as a two-component eyepiece, consisting of a field lens and an eye lens. The plane surface of the field lens should face the object glass, and the plane surface of the eye lens should face the eye, so that the two convex surfaces are facing each other. Keep looking through the telescope and move the field lens slowly towards you, just enough that the dust, etc., becomes sufficiently out of focus that it is not visible. Do not go any further than this, for you are introducing lateral chromatic aberration the more you move the field lens.

Jesse was also involved in manufacturing static electricity generation machines. According to http://www.sparkmuseum.com/FRICTION_HIST.HTM One of the earliest and certainly classic friction machines is the Ramsden machine, as pictured.

Construction A large circular plate of glass is mounted vertically on a metal axle, about which it can easily be turned by a crank handle. When passing between the two wooden supports, the surface of the glass is rubbed by two pairs of pads fixed to the supports. The rotation of the glass then causes it to become electrified positively on both faces. The negative charge of the pads is neutralized by being connected to the ground through the frame, which is not insulated. Each pad is stuffed with hair, and is covered with leather: Its surface is coated with mosaic gold, or an amalgam of mercury with zinc, bismuth, or tin. Attached to the pads are silk cases which enclose the glass plate nearly as far as the combs, these are to prevent loss of charge.

Once the electrical differential has been produced by the action of the pads on the glass, the charge must be collected in some way. Most friction machines do this via prime‑conductors. They consist of two long brass cylinders terminated at each end by knobs, and insulated by glass legs. These cylinders are connected to one another (at the opposite end from the plate) by a metal rod. The ends of the conductors nearest the machine carry metallic combs bent round and brought with the points close to both faces of the glass plate, but not quite touching it (Franklin's points).

Operation When the handle of the machine is turned the glass plate is charged positively by friction against the pads; while in this state it acts by influence (inductance) on the conductors, repelling a positive charge to the ends of the conductors, and leaving the parts nearest to it, the combs, negative.

The negative charge sets up an "electric wind" at the points of the combs, producing a continual discharge between the surface of the glass and the prime‑conductors. The glass is continually being re‑electrified positively by friction with the pads, thus causing an accumulation of electricity on the conductor.

An electroscope may be placed on one of the conductors in order to show the increase of the charge of the electricity.

To insure the proper working of the machine it is always necessary to have the room warm and dry; the glass legs supporting the conductors should be well cleaned before use, and wiped with a warm piece of flannel with a little paraffin oil upon it.

References:

http://chem.ch.huji.ac.il/~eugeniik/history/ramsden.html
Ramsden Eyepiece description http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/eyepiece.html
http://www.makingthemodernworld.org.uk/stories/enlightenment_
and_measurement/05.ST.05/?scene=4

http://www.makingthemodernworld.org.uk/people/BG.0100/

For further details and measurements obtained from the triangulation base lines, see http://www.sacred-texts.com/earth/za/za40.htm

Biography:

Jesse's biography is described at http://microscopy.fsu.edu/optics/timeline/people/ramsden.html and duplicated at http://www-history.mcs.st-andrews.ac.uk/Mathematicians/Ramsden.html , and at http://en.wikipedia.org/wiki/Jesse_Ramsden.

October 6, 1735 – November 5, 1800.

Born in Salterhebble near Halifax, England [of the Huddersfield, West Yorkshire Ramsdens]

After serving his apprenticeship with a cloth-worker in Halifax, he went in 1755 to London, where in 1758 he was apprenticed to a mathematical instrument maker. About four years afterwards he started business on his own account and secured a great reputation with his products. He died at Brighton.

Ramsden's speciality was divided circles, which began to supersede the quadrants in observatories towards the end of the 18th century. His most celebrated work was a 5-feet vertical circle, which was finished in 1789 (background image in portrait) and was used by Giuseppe Piazzi at Palermo in constructing his catalogue of stars. He was the first to carry out in practice a method of reading off angles (first suggested in 1768 by the duke of Chaulnes) by measuring the distance of the index from the nearest division. line by means of a micrometer screw which moves one or two fine threads placed in the focus of a microscope.

Ramsden's transit instruments were the first which were illuminated through the hollow axis; the idea was suggested to him by Prof. Henry Ussher in Dublin. He published a Description of an Engine for dividing Mathematical Instruments in 1777.

Ramsden is also responsible for the achromatic eyepiece named after him, and also worked on new designs of electrostatic generators. He was elected to the Royal Society in 1786.

In c.1785 or so, Ramsden provided a new large theodolite for General William Roy, of the Royal Engineers, which was used for a new survey of the distance between Greenwich, London and Paris. This work provided the basis for the subsequent Ordnance Survey of the counties of Britain. For his part with Roy in this work he received the Copley Medal in 1795.

Octants and Sextants

(http://en.wikipedia.org/wiki/Sextant) A sextant is a measuring instrument used to measure the angle of elevation of a celestial object above the horizon. Making this measurement is known as sighting the object or taking a sight. The angle, and the time when it was measured, are used to calculate a position line on a nautical or aeronautical chart. A common use of the sextant is to sight the sun at noon to find one's latitude.

The scale of a sextant has a length of 1/6 of a full circle; 60°, hence the sextant's name. An octant is a similar device with a shorter scale, 1/8 of a circle; 45°, which was in use until 1767 when it was quickly replaced by the sextant. In 1767 the first edition of the nautical almanac tabulated lunar distances, enabling navigators to find the current time from the angle between the sun and the moon. This angle is however sometimes larger than 90°, and thus not possible to measure with an octant.

Hold the instrument vertically and point it toward the celestial body. Sight the horizon through an unsilvered portion of the horizon mirror. Adjust the index arm until the image of the sun or star, which has been reflected first by the index mirror and second by the silvered portion of the horizon mirror, appears to rest on the horizon. The altitude of the heavenly body can be read from the scale on the arc of the instrument’s frame.

The horizon and celestial object remain steady when viewed through a sextant, even when the user is on a moving ship. This occurs because the sextant views the (unmoving) horizon directly, and views the celestial object through two opposed mirrors that subtract the motion of the sextant from the reflection.

A sextant's view merges two views. One view is of the sky, through the mirrors. The other view is of the horizon. One uses a sextant by adjusting the arm and a worm adjustment until the lower edge of an image of a celestial body touches the horizon. The measurement is timed to occur on a time-mark spoken by an assistant with a watch. The angle of elevation is then read from the scale, a vernier and a worm adjustment screw, and recorded with the time.

After a sight is taken, it is reduced to a position by following any of several mathematical procedures. The simplest sight reduction is to draw the equal-elevation circle of the sighted celestial object on a globe. The intersection of that circle with a dead reckoning track, or another sighting gives a precise location.

Theodolites

(http://en.wikipedia.org/wiki/Theodolite) A theodolite (Amer. "transit") is an instrument for measuring both horizontal and vertical angles, as used in triangulation networks. It consists of a telescope mounted movably within two perpendicular axes, the horizontal or trunnion axis, and the vertical axis. These must be mutually perpendicular. The optical axis of the telescope, called sight axis and defined by the optical center of the objective and the center of the cross-hairs in its focal plane, must similarly be perpendicular to the horizontal axis. Both axes of a theodolite are equipped with graduated circles that can be read

The history of theodolites goes back to so-called plane table alhidades, devices allowing the graphical mapping of the terrain. These devices consisted of a plane table and a telescope mounted in a fork-like contraption or alhidade, allowing it to be aimed out of the horizontal plane. The whole assembly rested on a plane table, onto which graphing paper was attached; a ruler connected to the alhidade in such a way as to be always pointing in the same horizontal direction as the telescope, was then used to plot the direction to the target.

Triangulation, as invented by Gemma Frisius around 1533, consists of making such direction plots of the surrounding landscape from two separate standpoints. After that, the two graphing papers are superimposed, providing a scale model of the landscape, or rather the targets in it. The true scale can be obtained by just measuring one distance both in the real terrain and in the graphical representation.

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