732 THE RAMSDEN DIVIDING ENGINE. 



Ramstlen's machine for ciittiug the screws of his dividing engine ac- 

 curately (wliich will be referred to below), reduced these errors to a 

 minimum. 



JESSE RAMSDEN'S DIVIDING ENGINES. 



Jesse Ramsden was the son of an innkeeper, and was born near Hali- 

 fax, in Yorkshire, in 1735. While at school in his native county his 

 fondness for mathematics was observed. Although he served as an 

 apprentice to a cloth maker in Halifax for some time, yet at the age of 

 twenty-four he had become skillful in making mathematical and philo- 

 sophical instruments, and his success was so great that he was soon 

 able to open an extensive establishment in London. 



It is stated that JIamsden first had his attention called to the subject 

 of dividing engines in 1760, by the reward which was offered by the 

 English board of longitude to John Bird for his method of dividing. 



Ramsden was doubtless ac(]uainted with what Hooke, the Due de 

 Chaulnes, Hindley, and others had previously done, and before the 

 spring of 1768 he completed his first engine, having in 1760 constructed 

 a very superior sextant. 



This first engine had an indented plate 30 inches in diameter, and 

 was used to divide theodolites and other common instruments, and did 

 so with sufficient accuracy, but it was not satisfactory^ to Mr. Ramsden, 

 who, in 1774-'75, constructed the engine, with a plate 45 inches in diame- 

 ter, which is now in the U. S. National Museum. (See Plate I, from a 

 recent photograph.) 



This dividing engine, together with the cutting gear with which the 

 screws of this machine was made, were sold by the heirs of Ramsden 

 to Messrs. Knox and Shain, of Philadelphia, Pennsylvania, from whom 

 Prof. Henry Morton, president of the Stevens Institute of Technology, 

 Hobokeu, New Jersey, purchased them about 10 years ago. Dr. Mor- 

 ton has recently deposited these machines in the U. S. National 

 Museum. 



The test of this, Ramsden's second engine, which divided a sextant 

 for Mr, Bird's examination accurately, was so satisfactory "that the 

 board of longitude, ever ready to remunerate any successful endeavor, 

 and to promote the lunar method of determining longitude at sea," con- 

 ferred a handsome reward on the inventor on condition that the engine 

 should be at the service of instrument makers, and that Mr. Ramsden 

 would publish an explanation of his method of making and using it. 

 This he did in a quarto pamphlet in 1777, the i>refaeeto which was pro- 

 pared by Nevil Maskeline, astronomer royal, dated Greenwich, Novem- 

 ber 28, 177G. In the following extract from it the reasons for publish- 

 ing the pamphlet are given : 



"i\Ir. Ramsden, mathematical instrument maker in Piccadilly, was 

 paid the sum of £615, by certificate from the commissioners of longitude, 

 upon delivering to them, upon oath, a full and complete written explana- 



