THE PHOTO-MICKOGKAPHIC CAMEEA 143 



relation to the optical system. The stage is situated in the 

 position T, and any object that is to be examined is placed on it 

 with the surface under observation downwards. Focussing is 

 effected by moving the stage, the objective and the rest of 

 the illuminating system remaining stationary, and this con- 

 stitutes its chief feature ; the manner in which this is 

 effected is a distinct departure from existing practice. The 

 apparatus consists essentially of three parts, all of which are 

 mounted on an optical bench, viz. a stand with a tube carrying 

 the objective and illuminating system, and the object-stage ; 

 an electric lamp, usually a small arc light with an iris- diaphragm 

 and illuminating lenses ; and a photographic camera. The 

 upright S carries a tube for observation together with the 

 illuminating appliance, and also has on it all arrangements for 

 altering the various adjustments. The stage T is raised and 

 lowered by means of a rack and pinion, and also has a fine- 

 adjustment fitted to it as with an ordinary microscope. The 

 lamp is carried on a supporting upright S x , and is adjustable in 

 a vertical direction by means of a rack and pinion, and adjust- 

 ment is provided for centration of the arc itself, if that be used, 

 by means of the adjustment-screws m 1 and m 2 . The arrange- 

 ment is really intended for use in conjunction with the small 

 Leitz arc lamp already described, in which the carbons are 

 at right angles to one another. The camera portion itself has 

 no special feature : it is made in three sizes, capable of exten- 

 sion to 28, 50 or 100 centimetres, and entails the use of a fairly 

 high-power eye-piece when high magnifications are required. 

 The camera is supported on two uprights which are adjust- 

 able in the line of collimation. A mechanical stage is 

 fitted, and two milled heads impart to the stage a com- 

 pound cross motion, and the amount of this motion may 

 be read to one-tenth of a millimetre by means of two vernier 

 scales. As a means of finding any given spot on a piece of 

 metal the mechanical stage is provided with a sliding pointer, 

 the position of which can be ascertained and registered by a 

 scale. The mechanical stage in the later forms is built into 

 the apparatus to ensure greater rigidity. The opening in the 

 stage may be varied in size so that large or small specimens 

 can be supported on it. 



The following directions are those given by Messrs. Leitz for 



