274 The Microscope. 



ciety or universal screw. The focussing adjustment is worked 

 by a rod passing beneath the box to the rear end where it is at- 

 tached to a milled head. In use the instrument is placed hori- 

 zontally upon a table, with a lamp behind the stage of the mi- 

 croscope, the light being condensed upon the object by means 

 of an ordinary bulls eye condenser. The arrangement will be 

 made clear by a wood cut to be given in the next of this series 

 of papers. The merits of this form of apparatus are its simpli- 

 city and cheapness ; the demerits, great unsteadiness, render- 

 ing it useless for high powers, and the inability to vary the 

 amount of magnification without change of objectives ; there 

 being no bellows or other arrangement for lengthening or 

 shortening the tube. 



GLEANINGS FROM OUR EXCHANGES. 



C. H. STOWELL. 



THE BINOCULAR MICROSCOPE.— W. B. Carpenter says 

 that there is one curious thing about the binocular micro- 

 scope, it increases very greatly the focal depth. He has tried 

 this under every condition and has always found this to be so. 

 He says this is partly explained by the binocular prism halving the 

 aperture of the objective. This does not wholly explain ithowever; 

 for he says he asked a friend once to look through the binocular 

 with one eye only, the prism being in its place, and to focus the 

 objective for what he considered to be a medial distance; on 

 then asking him to open the other eye, the difference in the depth 

 of focus was at once observed ; it was considered that the in- 

 crease amounted to at least five times. Prof. Carpenter says he 

 has consulted with some of his friends on this subject, but could 

 never come to any satisfactory conclusion. — Queckett Club. 



The Microscope in the School- Room. — The writer says that 

 no one, who has not tried it, can form an adequate conception 

 of the mental quickening occasioned by showing a few selected 

 slides to classes in the school-room. Such specimens as the 

 scales on a butterfly's wing, the eye of a common insect, grains 

 of sand, the circulation of the blood, etc. Thus by reaching the 

 mind through the eye a lasting impression is made ; such an 

 impression as books and diagrams could never produce. He 



