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Jesse Ramsden (October 6, 1735 - November 5, 1800) was an English astronomical and scientific instrument maker.

Ramsden was born at Salterhebble near Halifax, West Yorkshire, England. 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.

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 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. He died five years later at Brighton, England.

The July 28, 1827 edition of The Mirror of Literature, Amusement, and Instruction, Vol. 10, Issue 266, contained the following short memoir:

It was his custom, to retire in the evening to what he considered the most comfortable corner in the house, and take his seat close, to the kitchen fireside, in order to draw some plan for the forming a new instrument, or scheme for the improvement of one already made. There, with his drawing implements on the table before him, a cat sitting on the one side, and a certain portion of bread, butter, and a small mug of porter placed on the other side, while four or five apprentices commonly made up the circle, he amused himself with either whistling the favourite air, or sometimes singing the old ballad of

"If she is not so true to me,

What care I to whom she be?

What care I, what care I, to whom she be!"

and appeared, in this domestic group, contentedly happy. When he occasionally sent for a workman, to give him necessary directions concerning what he wished to have done, he first showed the recent finished plan, then explained the different parts of it, and generally concluded by saying, with the greatest good humour, "Now see, man, let us try to find fault with it;" and thus, by putting two heads together, to scrutinize his own performance, some alteration was probably made for the better. But, whatever expense an instrument had cost in forming, if it did not fully answer the intended design, he would immediately say, after a little examination of the work, "Bobs, man! this won't do, we must have at it again;" and then the whole of that was put aside, and a new instrument, begun. By means of such perseverance, he succeeded in bringing various mathematical, philosophical, and astronomical instruments to perfection.

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.

• O'Connor, John J., and Edmund F. Robertson. "Jesse Ramsden". MacTutor History of Mathematics archive.
• The Mirror of Literature, Amusement, and Instruction], Vol. 10, Issue 266, The July 28, 1827, from Project Gutenberg