Francis Watkins Microscope. By E. M. Nelson. 143 



same construction.* Varley's f (1831) and Pritchard's % (1838) 

 Microscopes, made by Hugh Powell, were the last of this form. 



The arm is only attached to the limb by three small knitting- 

 needles — these can be seen in fig. 26, the centre one, upon which 

 the fine-adjustment screw-thread is cut, is the thickest, viz. 

 12 B.W.G., the other two, which are 17 B.W.G., act as guides. 



The mirror, 1| in. in diameter, is both plane and concave ; 

 this is a very early, if not the earliest known example of a plane 

 and concave mirror. 



The limb is a dovetailed prism ; this is probably the earliest 

 instance of its use in Microscope construction. 



The stage is 1 ' 4 in. wide and 2 in. deep, the distance of the 

 optic axis from the limb being 1^ in. The stage is unlike those of 

 other makers : on its upper side it has a spring-clip for " sliders," 

 and on the lower one to hold a tube. Attention has already been 

 called to the well designed spring-clip to hold the stage at any 

 place on the limb. 



The pillar is 4£ in. long, and it, like the stage, is of artistic 

 form. A single Microscope in form just like this one was presented 

 to the Society by Colonel Tupman in 1905 ; it was thought to have 

 been made by Lindsay,§ but now it is clear that it is by Watkins. 



This Microscope is packed in a very handsome box (6f by 

 5f by 2 in.) made of oak, covered with shagreen, the hinges and 

 clips being of silver. This ends the description of the Microscope 

 itself, but in the same cabinet there is packed, besides the shagreen 

 box, a solar projection apparatus, also made of silver. The projec- 

 tion Microscope was invented by Dr. Lieberklihn, and in 1740 

 exhibited by him in London. The Microscope passed through the 

 axis of a ball, which fitted in a socket in a window shutter ; the 

 Microscope was pointed directly to the sun, the projection being 

 effected by means of a single lens, i.e. the simple Microscope. 

 Le pere Cherubin d'Orleans had, iu 1671, placed a telescope in the 

 axis of a similar ball-and-socket in a window shutter for the purpose 

 of projecting the solar disk ; this may have suggested the idea of 

 the solar projecting Microscope to Dr. Lieberklihn. 



John Cuff,|| in 1743, greatly improved the solar projection 

 Microscope by fitting a mirror to it, and by arranging matters so 

 that the position of this mirror could be adjusted from the inside of 

 the room, so that it was capable of rotation by cat-gut passing 

 round a pulley, and its inclination could be varied by means of a 

 rod. It was, in brief, a simple form of heliostat, which could be 

 worked by hand. 



* See this Journal, 1903, p. 587, fig. 143. 



t Op. cit., 1900, p. 283, figs. 70-73. 



X Microscopic Illustrations, Goring and Pritchard, figs. 12, 17, 21. 



§ At y<? Dial near Catherine Street in y<* Strand. 



II Against Serjeant's Inn Gate in Fleet Street. 



