200 



THE AMERICAN MONTHLY. 



[October. 



— Messrs. H. R. Spencer & Co. have 

 recently patented a device to protect the 

 interior and backs of objectives from dust. 

 It would have been described before but 

 for the absence of the Editor from Wash- 

 ington, where he expected to receive an 

 objective with the protector ere this. It 

 consists of a thin piece of plate-glass pol- 

 ished, and mounted in a ring screwed into 

 the back of the objective. It is said to be 

 a valuable addition to a lens, as no doubt 

 it is, while not affecting the corrections or 

 interfering with the performance of the 

 objective in anyway. The plan will es- 

 pecially commend itself to all workers 

 who leave their objectives attached to 

 the stands, as dust is sure to find its way 

 to them, even under glass shades. 



— Mr. J. C. Lathrop, who has an abun- 

 dance of the wonderful BaciUaria para- 

 doxa available for study, desires to know 

 how to isolate the peculiar diatom for 

 mounting. He also wishes to know 

 whether it is common or not. As regards 

 the mounting, no doubt our readers can 

 give him the desired information. As to 

 its abundance, we can only say that about 

 New-York it is not regarded as an unusual 

 form in gatherings from salt or brackish 

 water. It would be of interest to know 

 how widely it is distributed in this coun- 

 try, and we ask our readers to give this 

 information. 



— At the National Museum Mr. Harry 

 English has been engaged for some time 

 in preparing and mounting atypical series 

 of vegetable fibres. Most of the mount- 

 ing is done in a mixture of glycerin and 

 water, which is thought to be the best 

 medium for the purpose. The collection 

 of mounted specimens will be exceedingly 

 useful when it is completed, as it is in- 

 tended that every species of vegetable 

 fibre in the Museum cases shall be 

 mounted for examination at any time, 

 thus obviating the delay of preparation. 



CORRESPONDENCE. 



Objectives — Pond Life. 



To THE Editor : — During the two years 

 during which I have read your Journal I 

 have looked for some expression from you 

 regarding the value of homogeneous im- 

 mersion lenses. From articles I am con- 

 vinced that they have a value, but whether 

 commensurate with their cost I do not feel 

 satisfied. A brief statement will show my 

 position. For years I have been a stu- 

 dent of gross anatomy and systematic 



biology. Two years ago I took up the 

 microscope and began histological work. 

 I have a good stand, but no powers above 

 a dry working \. I have come to a point 

 where this will not do all that I want. 

 Having no opportunity to make personal 

 observations and comparisons, I am in 

 doubt where it is best to purchase. A 

 Hartnack water immersion giving about 

 the power I want costs ^45, a Spencer 

 homogeneous -^^ about ^55, and so on. 

 Are the immersion lenses worth the price ? 

 I cannot expect a busy professional man 

 to have time for a personal answer. If 

 you can give me a hint through the Jour- 

 nal, it will help me much. 



The application I have made of some 

 hints in the Journal may be of interest. 

 A few months ago a correspondent sug-- 

 gested in the columns of the Journal the 

 placing of slides back to back, and then 

 suspending them from hoops in ponds. 

 I modify his plan by taking waxed paper 

 (from cakes of soap) and punching holes 

 slightly smaller than my largest covers, 

 then wrapping the paper about the slides 

 in such a way as to bring the holes in the 

 middle on each side ; then suspending the 

 slides, I secured growths on a space a little 

 smaller than my covers, and am able to 

 secure good mounts many times. I am 

 now making a new application which 

 pleases me much. Taking a slide with a 

 spot of growing forms upon it, I surround 

 it with a cleft ring, as in Hardy's viva- 

 rium, bind on another slip, as suggested,- 

 and the little world is ready for observa- 

 tion. 



[We will endeavor to answer our cor- 

 respondent's inquiry next month. Some 

 light will be thrown upon the question by 

 the article published in this number, on 

 'The Microscope as a Physical Instru- 

 ment.' — Ed.] 



Exchanges. 



[Exchanges are inserted in this column without 

 charge. They will be strictly limited to mounted ob- 

 jects, and material for mounting ] 



Echinus spines of various species offered to any 

 person who will send in return three good sections 

 ot the same. 



Box 630, Washington, D. C. 



Wanted — Diatoms on seaweeds and in muds, from 

 all the tropic seas. Offered a large quantity of fine 

 selected diatoms and other slides, or cash. 



J. C. RINNBOCK, 

 14 Simmering, Wien, Austria. 



Will exchange well mounted slides for others well 

 mounted. _ 



H. H. PEASE, 

 1271 Broadway, N. Y, 



