1885.] 



MICKOSCOPICAL JOUENAL. 



103 



much for their objectives of this 

 class, I was disappointed at not be- 

 ing able to test the performance of 

 some of them. The best test of an 

 optician's skill is the making of thor- 

 oughly good lenses which can be sold 

 at moderate prices. Judged by this 

 test, the Bausch and LomlD Compan} 

 have achieved a gratifying success. 

 Having used their ' student series ' 

 side by side with similar objectives 

 of foreign make, I am convinced that 

 it is scarcely possible to secure more 

 satisfoctory work for the same price, 

 and that it is very possible to get 

 poorer. 



Much more might be said of their 

 general exhibit, but there was one 

 feature worthy of special attention. 

 I refer to their newly-produced mi- 

 crotome. This is alinost a new de- 

 parture in this country, but one other 

 maker having attempted the produc- 

 tion of such a machine. The model 

 shown at New Orleans was a tenta- 

 tive one, and has since been much 

 modified and improved. It differs 

 from the foreign model most familiar 

 in this country in that the object- 

 holder has a 

 vertical mo- 

 t i o n , i m- 

 parted by a 

 micrometer 

 screw' work- 

 ing in the 

 bed of the 

 machine, 

 instead of 

 moving up- 

 o n an i n - 

 clined plane. 

 The object- 

 ho Ider is 

 firm, and 

 has univer- 

 sal motion 

 on three ax- 

 es. The mi- 

 crometer 

 screw is actuated by a large head 

 or wheel, upon whose edge are 

 notches into which a catch falls. 

 These notches are so spaced as to 



represent an upward movement of 

 the screw of tj„'oi7 of ii" inch. It is 

 thus easy by the clicks of the catch 

 to determine the thickness of the cut 

 section. The triangular, prismatic 

 block carrying the knife moves along 

 the side of an upright rising from the 

 centre of the bed. It is held steadily 

 in place by a weight fastened to the 

 end of a bent arm extending over the 

 side of the way. This throws the 

 centre of gravity below the way and 

 gives great steadiness. For some 

 reason this feature has been aban- 

 doned in the later forms. 



Whether the extreme delicacy of 

 work possible with the Thoma mi- 

 crotome can be secured with this can 

 only be settled by trial. So far as 

 can be judged by observation with- 

 out experiment good services may be 

 expected from the Bausch and Lomb 

 machine. It would seem desirable 

 that metric units should be used in 

 their micrometer screw, since not a 

 few American students already find 

 metric expressions more readily in- 

 telligible than fractions of the inch. 



The Mcintosh Galvanic Company, 



Fig. i6 



Mcintosh's Projection Microscope. 



of Chicago, have a large exhibit of 

 their manufactures, including Dr. 

 Mcintosh's projection microscope. 

 The accompanying cuts give an idea 



