94 The Microscope. 



of all the series is most remarkable. I have never before seen 

 it equalled in a dry objective. Taking the series as a whole I 

 regard them as the best dry objectives I have ever seen. 



At the present time it is fashionable to use foreign objectives 

 and continental stands. I have secured and used Zeiss' ob- 

 jectives from the lowest power (3 to 5 inches) up to 1-18 homo- 

 geneous immersion, for the last seven years, and they are ad- 

 mirable objectives. I have also had the opportunit}^ of exam- 

 ing Zeiss', Reichert's and Leitz's most recent work, and 

 from such examination I believe that the work of Messrs. 

 Spencer and Smith is fully equal to Zeiss' best, and is certainly 

 superior to any Leitz or Reichert objective I have ever seen. 



As to price Spencer & Smith's work is cheaper by far than 

 Zeiss's for the same grade, and I understand that Messrs. 

 Spencer & Smith have a new series of moderate angle now 

 nearly ready for the market that are quite as cheap, or cheaper 

 even, than those by Leitz. Cheapness, however, should be no 

 criterion in the purchase of an objective. Quality should be 

 the controlling element. 



These American objectives, as I understand, are all made of 

 the old crown and flint glass whose staying qualities are well 

 known. I am sure from personal inspection that some kinds of 

 the Jena glass deteriorate with age. I do not think that in the 

 matter of purchasing scientific instruments ihe notoriety of the 

 maker should cut any figure. It is simpl}^ a question as to 

 where the most value can be had for the least money. In this 

 respect there is, so far as objectives are concerned, no need of 

 going abroad. The purchaser of foreign objectives will, as com- 

 pared with the series I have just described, pay more and get 

 less than if he purchased at home. 



I shall in a future communication describe a new homogeneous 

 immersion 1-10 of 138° balsam angle. Respectfully, 



Chicago. M. D. Ewell, M. D., LL. D. 



Editor The Microscope : — 



The diatom Amphipleura pellucida is considered the most 

 difficult of all the diatoms to resolve into transverse strise. To 

 even a fine objective it is a test, and to be able to see its striae 

 so that there shall be no doubt as to their visibility, is some- 



