JOURNAL 



OF TlIE 



ROYAL MICROSCOPICAL SOCIETY. 



FEBRUARY, 1912. 



TRANSACTIONS OF THE SOCIETY. 



I — A Geometric Slide PJwtomicrograpliic Apparatus. 



By J. E. Barnaed. 



{Read November 15, 1911.) 



The principle of the geometric slide is, perhaps, quite well known 

 to the Fellows of this Society, but in case there should be any to 

 whom the subject is not entirely familiar, I propose to very briefly 

 indicate the principles involved. A full description of it is to be 

 found in Lord Kelvin and Tate's treatise on " Natural Philosophy," 

 p. 153. The description given there is in reference not only to 

 the geometric slide, but also the geometric clamp, which is founded 

 on tlie same general principles. 



As you are all aware, nearly all photomicrographic appliances 

 so far constructed require considerable accuracy of workmanship 

 even apart from their design. In the apparatus now shown, quite 

 the opposite idea has been in view. The object has been to depend 

 on design almost entirely, so that the workmanship involved is not 

 of a very high order, and is certainly not of the order usually 

 required in scientific, and particularly microscopic, instruments. 



The principle of the geometric slide depends in the main on 

 the method of supporting any part of the apparatus on three points. 

 Where any of the separate appliances require to be fastened down 

 or restrained from moving, apart from the whole of the apparatus, 

 the clamp is so arranged that it comes within the triangle formed 

 by the three points of support. A typical example, therefore, of a 

 geometric slide is to take two straight rigid metal rods as a main 

 line of support. When any appliance has to be clamped on to 



Feb. 21st, 1912 B 



