194 



THE AMERICAN MONTHLY 



[October, 



present themselves, and are perma- 

 nent, because the mounting fluid re- 

 mains saturated, having parted with 

 its excess only. 



Note. — Since writing the above I 

 have much improved upon medium 

 No. i6 bv substituting the very best 

 damar resin for the rosin ; that is to 

 say thickening to the consistency of 

 molasses, and by heat, boiled balsam 

 copaiba with the clearest tears of 

 damar. Slides of ethyl-aether of 

 gallic acid mounted in this No. 17 

 medium, greatly surpa-^^s in beauty all 

 former successes. 

 Baltimore, September, 21, 1883. 



EDITORIAL. 



All communications relative to business matters, 

 should be addressed to the publishers, S. E. Cassino 

 & Co., 41 Arch Street, Boston, Mass. 



Contributions, exchanges, and letters pertaining 

 to the editorial management, should be addressed to 

 the Editor, 53 Maiden Lane, New York.N.Y. 



Subscription-price, Ji.oq per year, in advance. 

 Subscriptions begin with the January number, unless 

 otherwise ordered. Address, S. E. Cassino & Co., 

 Boston. 



Testing Objectives. — The article 

 published this month on the above 

 subject is deserving of more than pas- 

 sing interest from the microscopist. 

 The method is one readily applied by 

 any experienced observer, and the 

 apparatus required is inexpensive. 

 Any of the dealers in microscopical 

 apparatus can furnish the Abbe test- 

 plates made by Mr. Zeiss ; Mr. Em- 

 merich being the agent of Mr. Zeiss 

 in New York, will undoubtedly have 

 them in stock. The value of the 

 method is quite independent of any 

 theoretical consideration. It does 

 not offer a test which is only true if 

 the present theories of microscopical 

 vision are true. Although it originated 

 in a more perfect knowledge of the 

 microscope, springing mainly from the 

 investigations of Prof. Abbe, than was 

 hitherto possessed even by the most 

 learned physicists, it affords a means 

 of examining the image formed by the 

 objective, and indicates imperfections 



in the image which must be regarded 

 as such without regard to any theory. 

 Consequently it affords a means of 

 comparing different objectives, which 

 gives results beyond the influence of 

 the opinions or predilictions of the ob- 

 server, and which, in the hands of a 

 conscientious person, enables the rel- 

 ative excellence of different objectives 

 to be determined, and definately 

 stated. How long it will be before 

 this method is in general use by mi- 

 croscopists it is impossible to say, but 

 its advantages are so great, especially 

 for those who wish to purchase 

 thoroughly good objectives, and in 

 assisting those who are frequently 

 asked to express an opinion as to the 

 merits of objectives for inexperienced 

 friends or acquaintances, that we hope 

 to see it widely adopted in this pro- 

 gressive country. It may possibly be 

 true that in certain rare cases the 

 general efficiency of an objective may 

 be advantageously sacrificed to obtain 

 the greatest possible resolving power. 

 We would not wish to commit our- 

 selves to the opinion that this is ever 

 the case, but we admit the possibility. 

 Closing with the following quotation 

 from Dr. Fripp's article, we commend 

 it to the careful attention of micros- 

 copists : " The employment of the 

 test-objects most in use is, moreover, 

 calculated to lead to an entirely one- 

 sided estimation of the actual working 

 power of an objective, as, for example, 

 when ' resolving power ' .is estimated 

 by its extreme limits rather than by its 

 general efficiency ; or ' defining power,' 

 by extent of amplification rather than 

 by clearness of outline. So that an 

 observer is tempted to affirm that he 

 can discern through his pet lens what 

 no eye can see or lens show." 



The Distribution of Life in the 

 Sea. — At the Great International 

 Fisheries Exhibition, in London, among 

 the various forms of apparatus used 

 in deep-sea research there is shown, 

 in the United States Section, a copper 

 cylinder about two feet in length by 

 one foot in diameter attached in a pe- 



