30 Amen'cafi Quarterly Microscopical Journal. 



tive I have seen. The mechanical work is very good, the 

 appearance neat, and the lenses, when tested on the artificial 

 star, appear to be very well centered and figured, and the coma 

 is inward and not excessive. So far as could be judged from 

 outside appearances, for I made no attempt to unravel its 

 mysteries of structure, it is what is now called a " three- 

 system " objective, though M. Zeiss in his circular mentions it 

 as a "four-system" ; the front lens is, apparently, too large 

 for any " four-system " construction of equivalent focus. Con- 

 sidering the inexpensive character of the mounting, compared 

 with the elaborate and nice workmanship required for the 

 mounting of a first class juth or ^th, this objective is put at 

 an exceedingly high price — 240 thalers in Jena, say 60 dollars 

 gold, to which must be added duties, etc., if imported in the 

 regular way. It ought to do superior work. The balsam angle 

 of this objective, /. e. the angle of the emergent cone in balsam 

 as actually measured, is the same as that of a yVth Spencer, 

 belonging to a gentleman of this place, which was made at the 

 same time with, and indeed is the same in every respect as the 

 two objectives I had sent to my friends in Europe. With this 

 objective I compared the new Zeiss, and also with a Jsth of 

 much larger balsam angle, not yet completed in its own 

 mounting, though finished optically. I beg here to say that I 

 am no partizan either of the Spencers, or of Mr. Tolles ; I do 

 not own an objective made by either of them, higher than a 

 yz of 35°. With my friend, who owns the "Zeiss," I believe 

 in the "survival of the fittest." I am only interested in seeing 

 fair play, and I am sure that neither M. Zeiss nor my friend in 

 Germany, who endorsed him so highly, in the comparison with 

 the American objectives, will question my right either to criti- 

 cize or to publish the result, so long as I state facts which rest 

 not alone on my own testimony, though I may be pardoned 

 for saying I deem that sufficient. The objectives were tried in 

 as precisely similar conditions as possible. The same frustules 

 of Amphipleura, the same light — alternately changing the objec- 

 tives, with direct (axial) light, and with oblique, by day light 

 and by lamp light. With the mirror alone, and with the 

 " Wenham reflex." And this not once, but a great many 

 times. The tests were both dry, and balsam mounted, Amphi- 

 pleura, and for the axial light I had a remarkably excellent 

 specimen of the Podura scale. With the day light used in any 



