WALTER ROSENHAIN 13^ 



the lamp being enclosed in a light, tight, but suitably ventilated, 

 case. If the lateral tube through which the light passes is made of 

 the right length, all that is necessary for setting up the illuminating 

 arrangement is to switch on the lamp and to place the small tube 

 almost but not quite in contact with the rim of the iris diaphragm 

 outside the illuminator. A diagrammatic section of this whole 

 arrangement is given in Fig. 1, and a photograph is shown in Fig. 2. 



For photographic purposes, the intensity of the illumination 

 obtainable in this way is not large enough to be convenient. The 

 author has endeavoured to use one of the small tungsten arc-lamps 

 known as '' Pointolite," as the source for critical illumination in 

 photography, by placing the lamp itself in the conjugate focu^ 

 position. But with the largest size of this type of lamp at present 

 available, the illuminated area is not large enough. It is to be 

 hoped, however, that a larger form of this lamp may become avail- 

 able, and in that case it will be possible to carry out the best kind 

 of micrographic work without the use of a system of condensers, 

 such as are employed at present. 



The arrangements for fine focussing of the microscope when used 

 for photographic purposes frequently present imperfections which are 

 annoying in use, and are liable to lead to the loss of photographic 

 material. Whether gearing or a cord serving as a belt are employed, 

 there is always apt to be some degree of lateral pull applied to the 

 microscope when the fine adjustment head is turned by the operator 

 working from the screen end of the camera. The author has devised 

 a very simple means of avoiding this difficulty and of leaving the 

 microscope free as soon as the operator's touch is removed from the 

 focussing rod. For this purpose, the focussing rod, extending along 

 the length of the camera, operates by means of a small belt, a 

 rotating spindle attached to an independent bearing carries on a 

 separate stand. This rotating spindle is so placed as to be axial 

 with the fine adjustment of the microscope, in whatever position 

 this may be situated. The end of the spindle nearest the microscope 

 merely carries a cross-piece consisting of a thin rod. Fixed to the 

 fine adjustment head of the microscope itself is a light tube of brass 

 or aluminium. In this tube are two longitudinal slots diametrically 

 opposite one another. The independent spindle above mentioned 

 runs down the axis of this tube, but the transverse rod has its ends 

 projecting through the slots of the tube, the slots being made a 

 little wider than the diameter of the rod. If now the spindle is 

 rotated bv the operator turning the focussing handle, no pull what- 

 ever is placed upon the fine adjustment of the microscope — the motion 

 of the spindle being transmitted to the fine adjustment through the 

 slots in the tube. In these circumstances, a pure turning moment 

 or torque is applied to the fine adjustment, so that there is no 

 tendency to displace the microscope. Further, if the belt connecting 

 the focussing handle to the moving spindle is slightly elastic, the 

 moment the pressure of the operator's hand is removed from the 

 focussing handle, the spindle and the transverse rod which it carries 

 will spring back by a very small amount. In this way, the rod is 

 brought out of contact with the tube, and the microscope is left 

 entirely free from contact with the focussing gear. 



