168 THE MICROSCOPE. [August, 



available. On the other hand, the larger stands of the continental 

 type, with elaborate adjustments and numerous accessories, 

 always produce the feeling that, notwithstanding their ingenious 

 designs and great efticiency, they are unfortunately clumsy and 

 somewhat overloaded, their traditional compactness being main- 

 tained at the cost of some unnecessary inconveniences. The pos- 

 sibilities of the English-American stand seem to be not yet realized 

 on the continent ; but the w^riter will venture the prediction that 

 there will be a revolution in this respect some time before the 

 next tricentennial. The reaction has evidently commenced 

 already in respect of accessories and incidental refinements of de- 

 tail. Such microscopical aids and comforts as mechanical stages. 

 elaborate sub-stages and sub-stage condensers, iris diaphragms 

 and rapid nose-pieces, which we have been using for a genera- 

 tion, more or less, with great satisfaction, but which we have 

 meanwhile heard constantly denounced by partisans of the con- 

 tinental method as needless luxuries and distracting toys, all these 

 we now^ see introduced and given a proper prominence by the 

 best continental makers. 'Tis w^ell. 



As to objectives, the progress of the present day evidently cen- 

 ters around, or stands in comparison with, the apochromatic sys- 

 tem. Of the success of the system there is no longer a reasonable 

 doubt, either as a scientific or as a commercial question. Char- 

 acterized by the employment of new varieties of glass, of extra- 

 ordinary optical properties, manufactured at Jena, and by the 

 substitution of fiuorite (natural fiuor spar) for crown-class in sev- 

 eral of the lenses, it corrected spherical and chromatic aberration 

 to an extent not before attained. Brought into existence by the 

 researches and experiments of Abbe and vSchott, and first success- 

 fully introduced at the Zeiss factory, in 1884, it is now adopted for 

 their highest grades of objectives by all the above-named makers, 

 except perhaps Watson ; and new series or varieties are being con- 

 stantly introduced.* The resolution of Ainfhifleura fellucida 

 in dots, which has been ably disputed and may be still doubted 

 by some competent judges, is well within the limit of their ca- 

 pacity. The writer was fortunate in being afibrded the rare 

 privilege of witnessing the official trial of the objectives by the 

 jury, at which time the Zeiss i-ioth (3.5 mm.) of n. a. 1.63, 

 with monochromatic sunlight illumination, showed the dots (or 

 "■beads") with beautiful distinctness and with perfect ease. They 

 were seen at a glance over a large partof tlie shell at once, always 

 alike and with remarkable freedom from any suspicion of uncer- 

 tainty ; and when lost by change of focus, or even by carrying 

 the instrument to another table and readjusting the light, they 



*Near the close of the exposition, after the report on awards was adopted and closed, a new 

 i-i2th (2 mm.) was received from Naclii't and informally examined by the jury, with there- 

 suit of calling out from them a special note of commendation. 



