1892.] MlCROSCOt^IOAL JOURNAL. 91 



An .41l-aroun(l Microscope. 



By Prof. S. A. FORBES, 



DIRECTOK ILLINOIS STATE LABORATORY OF NATURAL HISTORY, CIIAMPAUiN, ILL. 



Mv personal studies are of a kind to require a microscope 

 which mav he used (i) for the study of bacteria sHdcs, (2) for 

 the study of mounted slides of serial sections, (3) to search 

 through and examine carefully collections of minute alcoholics in 

 glass dishes, (4) to dissect animals under powers varying from 

 twenty to two hundred tliameters, and (5) to study pinned insects 

 in all positions. 



For the first purpose one must have a stand fitted to carry ob- 

 jectives of the highest power and the best ilkmiinating apparatus ; 

 for the second, something in the nature of a mechanical stage is 

 very desirable, but tiiis must have a far wider sweep than the or- 

 dinary geared stage ; for the third, one must be able to explore 

 rapidlv and with low power a large surface, moving back and 

 forth along parallel lines as with a mechanical stage, but with 

 much freer motion in all directions. The stage must also be 

 without surface projections or attachments, which would be in 

 the wa}" of a glass dish of considerable size. The instrument 

 must, further, stand erect, and yet must not be too higli to work 

 at sitting. It is a great advantage if both eyes may be used. 

 Fourth, for dissection hand-rests must be provided, and the mi- 

 croscope must usually stand erect, and should be a binocular. 

 Fifth, for entomological work a binocular is needed, with stage 

 socket for insect forceps, and with a large central opening in the 

 stage to allow the ready turning of the object without interference 

 of the pin or danger of injury to the specimen. As this large 

 opening will admit light beside the condenser in bacterial work, 

 it must be fitted with an adapter with a smaller, opening. In this 

 work, also, the rectangular movement of a mechanical stage is a 

 great convenience for bringing insects readily into the field. 



As I accomplish all these purposes perfectly by a single micro- 

 scope, it seems to me that this instrument must be adapted sub- 

 stantially to everN'thing which the biologist is likely to want to do 

 with a microscope, and that a description of it may interest many 

 situated similarly to myself 



My starting point is a Zeiss stand. No. i, with oculars i to 5 

 (No. 3 being divided for the insertion of a micrometer), and ob- 

 jectives ranging from A3 to an apochromatic 1-12, with the cor- 

 responding eye-pieces. For ordinary binocular work I have a 

 Zeiss binocular eye-piece, which has the advantage over any other 

 binocular arrangement that it does not so increase the height of 

 the instrument as to make it inconvenient to use it with low 

 powers while sitting. 



The special feature of the instrument is the stage, which is the 

 simplest form of a mechanical movement in two rectangular di- 

 rections, adapted to the square stage of my instrument as illus- 

 trated by the engraving accompanying. The stage plate of the 



