1882.] 



MICKOSCOPICAL JOUKNAL. 



225 



to the experiments of a few years ago, 

 the question has forced itself upon 

 several microscopists of this city 

 while examining objectives from dif- 

 ferent makers : '* What is the proper 

 appearance of the podura-scale ? " It 

 is not now a question of structure 

 but of appearance. It is found that 

 a Wales objective gives a different 

 appearance to the markings from a 

 Tolles. Both give sharp images, but 

 they are not alike. Which is the 

 best objective — in other words, which 

 image is the correct one ? It is dif- 

 ficult to describe the different ap- 

 pearances without illustrations, and 

 the purport of this article is merely 

 to direct the attention of observers to 

 the subject, as it is our intention to 

 return to it at some future time when 

 suitable cuts can be obtained. 



With some objectives each " excla- 

 mation point ", or spine as we shall 

 designate it, appears to have a longi- 

 tudinal slit of light, tapering at both 

 ends, the broadest part near the top 

 of the spine. With other objectives 

 the line of light appears to have a 

 distinct head at the upper end, from 

 which it tapers away. While some 

 objectives clearly show the point 

 where the spine seems to be attached 

 to the scale — that is, they very sharp- 

 ly define the tapering end of the 

 spine — others show only the upper 

 part of the spine, the small end being 

 " fuzzy " and fading away indefinitely. 

 It is not usual to see the spines just 

 as Mr. Beck has figured them. A 

 cheap Beck objective gives the near- 

 est approach to that appearance of all. 



In these observations, which were 

 made by several persons together, a 

 number of objectives of the same 

 nominal focal length, and of the same 

 angular aperture, were compared un- 

 der identical conditions, and others 

 of different powers were used with 

 oculars which afforded approximately 

 the same magnifying power. 



The result is, that it is still a mat- 

 ter of uncertainty how the podura- 

 scale ought to appear. 

 o 



Cleaning Diatoms. 



REPLY TO MR. KITTON. 



Having been absent in the moun- 

 tains, I did not see, till the latter part 

 of last month, the reply of Mr. Fred. 

 Kitton, Honorary F. R. M. S., in the 

 August number of the Journal, to 

 my article on " The Preparation of 

 Diatoms," published in the June 

 number. Though I had not unfre- 

 quently seen the Science Gossip, I had 

 never met with Mr. Kitton's articles, 

 nor heard of them till I saw his re- 

 ply. My article was actually written 

 about five years ago, and I then 

 showed it to Mr. Charles Stodder, of 

 Boston, Mass., well known to micro- 

 scopists, who advised me to offer it 

 for publication. I did not, however, 

 and it laid among my papers till I 

 took it up last March. With slight 

 revision, it is the same as I wrote five 

 years ago. Previous to 1877, I, in 

 correspondence, and verbally, related 

 the process as I have described it in 

 my article, and I have done so since 

 1877. After reading Mr. Kitton's re- 

 ply, I wrote to Mr. Stodder ; he 

 looked up Mr. Kitton's articles, and 

 he writes me (he had never seen 

 them before) that Mr. Kitton's de- 

 scription of the process is, indeed, 

 very like mine. I can only say, this 

 is coincidence. Had I known of Mr. 

 Kitton's articles I might not have 

 written upon the subject ; or, had I 

 written, I would have given him full 

 credit. My purpose in offering my 

 paper for publication was to present 

 a simple, clear, concise account of the 

 process from beginning to end, for 

 large quantities of material as well as 

 small, of the preparation of diatoms, 

 such as I had not found in books or 

 science publications, and such as I 

 thought most of those, beginners es- 

 pecially, interested in the study of 

 these beautiful objects, had not 

 found. The claim to originality lay 

 especially in the extended mode of 

 getting rid of the sand. The chemi- 

 cals I knew had been used be- 

 fore, if not in the same order. With 



