1897J MICROSCOPICAL JOURNAL 917 



stops for oblique lij^-lit, several annuli, and a g-round g-lass 

 stop, making- a compendium no doubt somewhat too g-reat 

 for the general worker, but which is very serviceable to 

 the experimentalists. 



As far as color discs are concerned the stops are so 

 arranged that all those which can be pulled out from the 

 left side of the carrier c^use the backg-round to be colored 

 whilst those which can be pulled out from the right side 

 cause the object to be colored. 



The number of effects which can be obtained with such 

 an apparatus is unlimited. Mr. Rousselet showed us some 

 weeks ago an ingenious color illuminator, by which, accord- 

 ing to a little mathematical calculation, 36 effects could be 

 obtained. By applying- a similar calculation to this arrang-e- 

 ment it would give some few hundred millions of combina- 

 ti<jns. ^Phis number may be too much even for an enthu- 

 siast, and one may prefer to pass over from the quantita- 

 tive to the qualitative use of the arrangement. 



I^^or simplicity in use it cannot be excelled, as it allows 

 of every kind of illumination and stop, being automati- 

 cally broug-ht into action whilst the object is under exami- 

 nation. The best result can, therefore, be obtained with 

 far greater ra]>idity than ordinarily, and comparisons can 

 l)e effected without having to bother about taking stops in 

 and out, as in the ordinary way. The apparatus, althoug-h 

 efficient, is needlessly clums}^ and heavy. The principle 

 can be easily adopted in a neater form, and made to fit any 

 condenser. 



How to Test Objectives is the subject tt) wiiich l)ut 

 few pharmacists and physicians pay much attention. In a 

 lengthy article on the subject by Dr. A. C. Stokes, pub- 

 lished in the Journal of the New York Microscopical Society, 

 the writer says : "A severe test, then, or one that should 

 come within the ability of the objective, and so fulfil the 

 conditions of the ideal object for the purpose, is, for a 

 first-class four-tenth-inch, the black dots of Pleurosioma an- 

 gi/latum in balsam, and perhaps, and imperfectly, the secon- 

 dary structure of Arachnoidiscus E/ire>it>eri;ii •, for a one-fifth 



