PROCEEDINGS OF THE SOCIETY. 729 



taking Wollaston doublets. The Microscope is therefore a " single and 

 double," to use the terminology of that day. 



The mirror has its pivots sprung. This kind of springing was first 

 used by Powell in the stage forceps of a Microscope he made fur 

 Cornelius Varley in 1831.* 



The rackwork coarse adjustment has a sprung pinion ; this device 

 was first used l>y Powell in the " Vial Microscope" which he made for 

 C. Varley in 1883. f 



The stage is very important ; it is supported by brackets after the 

 manner of Valentine's Microscope made by Andrew Eoss in 1831. It 

 has a Turrell stage (first made in 1833). It has also stage focussing by 

 three wedges which are moved by a micrometer- screw having its head 

 divided into 25 divisions, the movement being T i__ in. for one complete 

 revolution of the micrometer-screw. This he described in the Trans. Soc. 

 of Arts, vol. 50, pt. 2, p. 108, the plate being in vol. 49 (1833). 



The stage has also a micrometer movement by means of a T ^ thread- 

 screw, the head being divided into 100 parts, each part therefore being 

 equal to to^ou i Q - The second or " B" eye-piece has a cobweb across 

 it, which can be focussed to the eye-lens or put out of focus when not 

 required. The method of using the micrometer is therefore to place 

 the object to be measured so that its image touches the cobweb in the 

 eye-piece, and then by means of the graduated micrometer-head the 

 object is moved across the cobweb, and its size directly determined. 

 This kind of micrometer was designed by Fraunhofer and, a description 

 will be found in Hannover on the Microscope (English translation, 1853, 

 p. 67, fig. 12, pi. 1). This micrometer was one of the best in the days 

 before the advent of accurately ruled glass micrometers, and before the 

 introduction of the achromatic lens, when microscopic objects were some 

 sizes larger than they are now. 



The eye-pieces are capped, the tube being the same diameter as that 

 of the body ; the caps have a bayonet-joint catch. There is an achro- 

 matic substage condenser with rackwork focussing by means of a sprung 

 pinion. 



The presence of the condenser prevents the Microscope being dated 

 earlier than 1839. We therefore know its age within the narrow limits 

 of (1839-41). 



(3) John Cuff's Microscope, presented by Curties. The date of its 

 introduction was 1744. Cuff was an optician in Fleet Street. It was 

 called A New Constructed Double Microscope, and is in this respect 

 peculiar, because a great many instruments of that time were either 

 single Microscopes, or double and singles. To translate this into present 

 day terminology, for " double " read " compound," and for " single " read 

 " simple." The box-foot of John Marshall (1704) is retained. In fact 

 the whole instrumeut is a small and simplified edition of John Marshall's 

 Microscope. It was a very good and popular Microscope, and was still 

 made in 1798 by Jones, the successor to Adams. These instruments 

 signed by Cuff must be rare, as Cuff disappears from the scene ; for his 

 Microscopes were copied by Adams in 1771, so that it is probable that 



* Trans. Society of Arts, vol. 48, p. 332, pi. 4 (1831). 

 t Ibid., vol. 50, p. 158, pis. 5 and 6 (1834). 



