80 



THE AMERICAN MONTHLY. 



[April. 



tion with a region where cholera pre- 

 vailed ; and, further, that the disease from 

 an infected locality never yet passed on to 

 another place if the journey lasted a cer- 

 tain time without interruption. The large 

 intercourse between India and Europe, 

 more particularly England, by means of 

 ships which sailed round the Cape of 

 Good Hope, had never succeeded in 

 carrying cholera from India to England.' 



CORRESPONDENCE. 



Concerning Angles. 



To THE Editor : — * * * In the No- 

 vember number of the Journal, 1884, 

 under the head 'Choosing Objectives,' you 

 make the statement that a ' Hartnack 

 water-immersion at $45 probably will not 

 do what the Spencer homogeneous immer- 

 sion at 1:55 will do.' I have been work- 

 ing with wide angle homogeneous objec- 

 tives for the last three years, and I have 

 Tolles ^^ and I each 126° B. A., and my 

 experience is simply this, that no water- 

 immersion objective that I have examined 

 is in any respect their equal for histolog- 

 ical work or anything else. I use the 

 microscope daily, and have had several 

 hundred dollars worth of various grades 

 of objectives to examine. Now, as a 

 matter of fact, I ordered of Dr. Chase a 

 Spencer ^^ of 100° b. a. which you so 

 highly recommended in the Journal, and 

 I can say that it was one of the best high- 

 powers I had examined ; yet it did not 

 do the work of the Tolles ^\y or I, so I ex- 

 changed for a Spencer -j^^^ of 115° b. a. 

 I consider this y"^ of 115° B. A. worth 

 about twice as much as the one of 100° b. 

 a. For all ordinary work its resolution is 

 greatly superior to the one of a 100° b. 

 a., its working distance is ample, its defi- 

 nition and resolution are all that could be 

 expected for the angle. 



Another statement made in the article 

 above mentioned is this : — ' Even for those 

 refined studies of bacteria and diseased 

 germs, which have attained such great 

 importance at the present day, these ob- 

 jectives [water-immersion] are to be most 

 highly recommended.' One question may 

 be asked here, is it possible for a low or 

 medium angle water-immersion objective 

 to give as sharp and clear definition of 

 those minute organisms as a first-class 

 homogeneous-immersion objective of high 

 angle can? I have tested both kinds of 

 objectives with bacteria, salivary corpus- 

 cles, and histological slides of various 

 kinds, and I will have to see the water- 



immersion objective that is in any respect 

 the equal of a well-constructed homoge- 

 neous-immersion objective of 126° b. a. 

 They, water-immersion objectives, are 

 useful on very thick histological sections, 

 because their working distance is greater 

 then high angle homogeneous objectives 

 of high power. I have a Tolles ^ of 126° 

 B. A., which works easily through three 

 and four thin cover-glasses, and I deem 

 it one of the best histological lenses ever 

 made. I can examine almost anything 

 with it. It resolves Amphipleura in bal- 

 sam beautifully, and can do the work of 

 any ordinary dry \. Now, in conclusion, 

 I will state that of all the objectives I have 

 examined, I found none equal to Tolles" 

 or Spencer's best work. The Journal 

 has been a welcome visitor to me for the 

 last three years. I deem it a most useful 

 publication. Pierce Tyrrell. 



Elgin, 111. 



NOTICES OF BOOKS. 



Second Annua/ Report of the Btireatt of 

 Ethnology to the Secretary of the Smith- 

 sonian Institution, i88o-'8i. By J. W. 

 Powell, Director. Washington : Gov- 

 ernment Printing Office. 1883. (4to, 

 PP- 477-) 



Among the many publications of a 

 scientific character issued by the authority 

 of the United States Government, few can 

 compare in general interest, or in excel- 

 lence of form, with the two reports of the 

 Bureau of Ethnology, under the able di- 

 rection of Major Powell. . It is impossible 

 to condense within the few lines that can 

 be here accorded to notices of books, 

 anything that will convey even a faint 

 idea of the varied contents of this, the 

 second large volume. Ethnology includes 

 a vast range of subjects. We find here 

 the results of long study of the languages 

 and customs of the aborigines of America, 

 of their folk-lore and strange myths, 

 superstitions, and religion, their arts and 

 industries. The volume includes an il- 

 lustrated catalogue of the collections ob- 

 tained by Mr. James Stevenson from the 

 Indians of New Mexico and Arizona. 



Exchanges. 



[Exchanges are inserted in this column without 

 charge. They will be strictly limited to mounted ob- 

 jects, and material for mounting.] 



Palates of molusca in exchange for other objects, 

 mounted or unmounted. 



A. B. AUBERT, 

 Orono, Penobscot County, Maine. 



