of the late Mr. Ramsden. 255 



might occasion in the longitude an error of fifty nautical 

 leagues. Mr. Ramsden therefore changed the construction 

 in regard to the centre, and made these instruments so cor- 

 rect as to oive never more than half a minute of uncertainty- 

 At present he warrants sextants of fifteen inches radius 

 to within six seconds. Since the time when he Kmproved 

 these instruments he has constructed 983 ; and several of 

 tliem having been carried to India and America, the error 

 has been found to correspond with what he determined it to 

 be before their departure. He has since made sextants from 

 fifteen inches to an inch and a half radius, and in the latter 

 the minutes can be clearly distinguished; but in general he 

 prefers those of ten inches, as being easier managed and 

 susceptible of the same exactness. 



The invention of a dividing machine having now become 

 necessary, he employed himself in constructing one, whicli 

 he did vvith the greatest success. The dividing machines 

 before used were far from being exact. Graham and Bird 

 employed beam compasses. The latter kept his method 

 a secret till it was purchased from him by the board of lon- 

 gitude, in order to be published. Mr. Ramsden had already 

 discovered a method of his own, which in exactness sur^ 

 passed that of Bird. For large works he still uses the 

 beam compasses ; but as it is necessary in the greater num- 

 ber of conunon instruments to save time, he has employed 

 himself for ten years in improving his dividing machine, in 

 which ease and expedition are united. You have seen that 

 admirable machine with which a sextant could be divided in 

 the course of twenty minutes, and which is sufficient to give 

 an idea of the inventi\'c genius and superior talents of Mr. 

 Ramsden. It was your friend Dr. Shepherd who made this 

 excellent machine known to the board of longitude, who 

 gave the inventor a premium of 6OOI. sterling, and caused 

 an engraving to be made of it in 1777 : hut the edition was 

 accidentally burned, and von are right in wishing to cause it 

 to be engraved at Paris. The machine is still in the hands 

 of Mr. Ramsden, and he has undertaken to divide sextants 

 for three shillings. The board of longitude has often given 

 greater premiums for objects of less utihty ; but the greatest 

 men do not aluays obtain the greatest rewards. Newton, 

 indeed, got a place in the mint; but lie was not indebted 

 for it to his merit alone. 



Mr. Raniiden has constructed an instrument also for di- 

 viding straigh; lines, a description of which has been printed ; 

 and I am sorry ibat you have no longer at Paris that invented 

 by M.Megnie, ui order that they might be compared. 



While 



