lyODj iMUniOSCUPJCAL .lOUitlNAL. 313 



essarily less bulky, and therefore less expensive, than is 

 the case when a table microscope is employed, which is a 

 set-ofi' against the extra cost of a special form of micro- 

 body and stage. Besides this, unless the operator hap- 

 pens to possess two microscopes, he can ill-spare his in- 

 strument for photography, as he needs it constantly for 

 the visual «^xaunnati()n of his specimens. 



I do not employ a rod and pulleyiu connection with the 

 fine adjustment, as the limited camera extension admits 

 of this being manipulated at arm's length without incon- 

 venience. In many forms of photo-micrographic appa- 

 ratus, the microscope and illuminating system are swung 

 upon a centre so as to enable the worker to visually ex- 

 amine his specimens before photographing them. I have 

 adopted the more simple plan of introducing a rectangu- 

 lar prism between the two lenses of a Huyghenian eye- 

 piece, so that the object can be viewed from the side of 

 the microscope, and any desired portion brought into the 

 field of view. 



The stage that I have briefly described is a very sim- 

 ple and inexpensive form, with substage tube at the back; 

 but I confess that for medium or high-power work it 

 would be a great comfort and convenience to have also a 

 rotating mechanical stage, backed by a sub-stage having 

 centring screws and rackwork to take achromatic or apo- 

 chromatic condensers. 



One last word about illuminating apparatus. Practically 

 we have a choice between sunlight, limelight, and acety- 

 lene or paraffin-lamp light. With the intensely brilliant 

 parallel rays of the sun reflected from a mirror or helio- 

 stat, no system of converging lenses is needed save that 

 of the chromatic condenser in the substage. The rays 

 brought to a focus even by a lens of small aperture are 

 liable to injure a balsam-mounted specimen, and lam not 

 certain that they do not act injuriously upon some of the 

 glasses employed in modern objectives. I find, however, 



