88 SCIENTIFIC SURVEY OF YORK AND DISTRICT 



similar business in Aldersgate Street, London, and became established at 

 136-138 Fleet Street. During this partnership the historic 36-in. 

 theodolite was constructed for the great Trigonometric Survey of India. 

 The firm retained the name of Troughton & Simms through the partner- 

 ships which followed up to 191 6, when it became incorporated. It is 

 probable that the introduction of the micrometer microscope by Edward 

 Troughton was the most important advance ever made in the scientific 

 comparison of measures of length. The instrument, although of simple 

 construction, was capable of determining differences of length of one 

 ten-thousandth part of an inch. Troughton's 5-ft. scale also has 

 become historical owing to its great accuracy. 



Of Thomas Cooke, founder of the branch of the firm bearing his name, 

 Samuel Smiles relates that as an amateur he made his first object glass out 

 of the bottom of a thick glass tumbler. He began the manufacture of 

 refracting telescopes in 1836 at York. About 1852 he commenced making 

 turret clocks and effected many improvements in them. In 1855 

 Buckingham Works were established. In 1868-70 he constructed what 

 was then by far the largest equatorial refractor in the world (25-in. 

 aperture). This instrument, the Newall telescope, is still in regular use 

 at Cambridge Observatory. Cooke early turned his attention to the 

 design and manufacture of surveying instruments ; the first important 

 meridian instruments made by him were a pair of 5-ft. transits for the 

 Trigonometric Survey of India. 



The ' Cooke ' photographic lens is known all over the world ; his 

 surveying instruments have played their part in connection with such 

 engineering achievements as the Forth Bridge, the Assouan Dam, etc. 

 Captain Scott located the South Pole with a Cooke theodolite. The 

 Franklin- Adams star charts owe their excellence to the fact that they were 

 taken by means of Cooke astro-photographic lenses on an equatorial 

 mounting of the English type specially made by this company. 



In 1922 a fusion was effected between these two old-established firms 

 under the name of Cooke, Troughton, & Simms, Ltd., with works at 

 York and at Charlton, London, S.E. 17. 



Opportunities will be given to the members of the British Association to 

 visit the works at York. All the optical work of the firm is done at the 

 York factories, and a representative selection of the following optical glass 

 work will be on exhibition : Mangin mirrors, heliograph mirrors, spherical 

 mirrors, astronomical objectives, small telescope objectives, microscope 

 objectives, various types of lenses and prisms. A general selection of 

 surveying instruments will also be shown, including the ' Tavistock ' 

 double-reading theodolite, and a new transit instrument (under con- 

 struction) for Greenwich Observatory. 



