1886.] 



MICEOSCOPICAL JOURNAL, 



7T 



described* a new objective constructed 

 by Mr. Zeiss with some new glass of 

 high refractive power which has re- 

 sulted from numerous experiments 

 conducted by Professor Abbe. From 

 the article referred to we compile this 

 brief notice. The desired qualities 

 of glass not being obtainable from 

 manufacturers, Mr. Zeiss, aided by 

 a liberal subsidy from the government, 

 courageously undertook to make it. 

 He put up a glass furnace and finally 

 produced what was required. 



The objective is a ^-inch, n. a. i .4. 

 This is not so high a numerical 

 aperture as has been obtained in 

 England, where i .5 has been reached ; 

 but the Zeiss objective is decidedly 

 superior to the other because the new 

 glasses permit of more pei'fect cor- 

 rection of the aberrations. With the 

 vertical illuminator the silvered A. 

 pelhicida is resolved in beads over its 

 entire surface with such purity that 

 each bead may be counted. In addi- 

 tion to the objective, Mr. Zeiss has 

 also made several oculars with the 

 new glasses which also possess great 

 advantages over those in use, partly 

 due to the construction. One of them, 

 intended to be used instead of the 

 ordinary amplifier for projection and 

 photography, is composed of a slightly 

 biconvex field lens combined with a 

 plano-concave at a proper distance, 

 with a diaphragm above. The dis- 

 tance between the two lenses is regu- 

 lated by a delicate adjustment. After 

 focussing with an ordinary ocular, 

 the latter is replaced by the projecting 

 ocular and, without changing the 

 focus, the image is made perfectly 

 sharp on the screen by moving the 

 upper lens of the ocular. 



The Rotifera or Wheel Ani- 

 malcules. — This is the title of a 

 valuable and elegant woi'k now be- 

 ing published by Messrs. Longmans, 

 Green & Co., London. The authors 

 are C. T. LIudson and P. H. Gosse, 

 both well-known workers in this in- 



* Moniteur du Praticien, February, 1886. 



teresting field. In the publishers' an- 

 nouncement it is stated that : — *• The 

 two authors, independently of each 

 other, had for many years been accu- 

 mulating materials for a monograph 

 on the Rotifera, or Wheel- Animal- 

 cules, and had almost abandoned the 

 intention when they chanced to be- 

 come . acquainted with each other's 

 design, and then found that, by a 

 great piece of good fortune, their 

 respective stores of notes and draw- 

 ings to a large extent supplemented 

 one another, and that they had thus 

 between them observed and drawn 

 the whole of the known British 

 species. 



o 



Some New AND Rare Diatoms. — 

 We are indebted to Messrs. 'W. C. 

 Walker, of Utica, and H. H. Chase, 

 of Geneva, N. Y-, for the first part 

 of a folio publication which they pro- 

 pose to issue as occasion may require, 

 describing new and rare diatoms. 

 The part before us includes seven 

 folio pages of printed text descriptive 

 of the species, and two photograph 

 prints from drawings, mounted on 

 cards of the size of the pages. The 

 authors do not undertake this meri- 

 torious work with the intention of 

 making money by it, but they are, 

 nevertheless, we believe, not averse 

 to receiving numerous orders, which 

 will materially aid in paying the ex- 

 penses of what must be a rather ex- 

 pensive undertaking. The illustra- 

 tions are certainly entirely satisfac- 

 tory, but we cannot understand why 

 the negatives are not taken directly 

 from the objects instead of from draw- 

 ings. No doubt there are good 

 reasons for the plan adopted, but at 

 first thought it w^ould seem to in- 

 volve considerable unnecessary 

 labor in making drawings. Orders 

 should be sent to either of the 

 authors whose addresses are given 

 above. We bespeak a hearty sup- 

 port of this enterprise by micro- 

 scopists generally, and especially by 

 tlie large number of those interested 

 in diatoms. 



