and Laboratory Methods. 



1155 



of slides is also arranged numerically, the accession catalog being the one 

 devised by Dr. Ward. The subject card catalog makes it comparatively easy to 

 locate the slides of any particular subject. 



Between the museum and the general laboratory is a room in which is placed 

 the department library, where are kept all the working books on biology. To 

 this the students of the department have free access at all times. 



The storerooms of the department are located upon the north side of the 

 basement. Upon the south side of the basement are two rooms for botanical 

 laboratories. On the south side of the basement, also, is located the vivarium, 

 in which are kept the animals which must be kept in stock for the biological 

 laboratory. This room is floored with cement, inclining towards an opening in 

 the center which is connected with the sewer, so that by means of a hose the 

 room can be thoroughly flushed and cleansed. Connected with this room is the 

 injection room, which has a cement floor arranged in the same manner. In this 

 room all the dirty work of killing large animals and of injection, in fact all work 

 which would be liable to foul the laboratories, is taken care of. In this way a 

 large part of the disagreeable work is kept out of the laboratory rooms. 

 Ripon College. C. DwiGHT MarSH. 



A Combined Condenser and Polarizer for Petrographical 



Microscopes. 



The attachment consists of a double lens condensing system, and a Nicol 

 prism mounted as shown in the following illustration. 



The upper condensing lens is mounted 

 on a revolving arm so that it may, at the 

 will of the operator, be instantly thrown in or 

 out of the optical axis by a lever ; a suitable 

 stop bp'ng provided to bring it to a central 

 positi .ii. 



The lower lens is mounted at the proper 

 distance below the upper surface of the appa- 

 ratus so that when the upper lens is moved 

 out of optical axis, the lower lens focuses upon 

 the slide, thus avoiding the necessity of re- 

 focusing the condenser system when changing 

 from the double to single combination. The Nicol prism is mounted in 

 revolving sleeve with graduated collar and a stop to indicate zero or the position 

 of Nicol prisms when crossed. 



The advantages of this arrangement over others for accomplishing the same 

 results are, briefly, as follows : 



First — It is not necessary to increase the size or thickness of the microscope 

 stage. 



Second — The attachment is always in focus whether one or both lenses are used. 

 Third — Compactness and freedom from liability of disturbance while operat- 

 ing stage or slide. W. L. Patterson. 



