PROGRESS OF MICROSCOPICAL SCIENCE. 43 



Extraordinary Microscopy. — In a journal published in Philaclelpliia 

 called the ' Medical Times,' whicli is remarkable for several able and 

 interesting medical papers, we find an extraordinary communication 

 (March No.) by Dx*. Neulenz. The following quotation will give our 

 readers some idea of this gentleman's opinions. We are a little sur- 

 prised at their making their way to so great an extent as a column 

 and a half in such a paper as the ' Medical Times ' : — " Having 

 constructed a one-seventieth immersion objective, on a new prin- 

 ciple, having 191° aperture, — the immersion liquid being fluoric 

 acid, — and, for illumination, having invented a new eccentric 

 parallolopiped, to be used with fluorescent rays exclusively, some 

 remarkable results have been obtained. I take great pleasure in 

 stating that, with regard to test-objects, all previous observers have 

 been totally wrong in every particular, and that Pleurosigma angidatum 

 is, in the first place, constructed on the plan of the Nicholson pave- 

 ment, and, in the second place, that it is not a Pleurosigma at all. 

 The most certain test-object is the Newlenzia cUfficilissima, a very rare 

 and remarkable diatom, in which my one-seventieth with the parallel- 

 epiped shows four kinds of beads and six sets of cross-lines, one of 

 which sets contains 147,229,073 lines to the inch : hence, by the 



well-known formula of Brewster, -^^— = ^ o .x .p .y, it is impossible 



that the undulations of light should pass without being previously 

 deflagrated, and therefore no other lens can possibly show these lines, 

 nor is it probable that this lens would with any other observer. The 

 immense superiority of this test to Nobert's plate is apparent." 



Note on AmpMplem-a pellucida. — Assist.-Surgeon Woodward, who 

 may be said fairly to take first rank among American microscoj)ists, 

 has contributed a paper on this subject to ' Silliman's American 

 Journal' for May. He says the attention of microscopists has fre- 

 quently been directed, of late years, to the Amphipleura pellucida or 

 Navicula acus, as a test-object well suited to try the defining powers 

 of the very best object-glasses. The length of this diatom is stated 

 by Pritchard as ranging from -j^oth to ^^th of an inch. The 

 average length is given by the ' Micrographic Dictionary ' at '0044 of 

 an inch. The striae, which are exceedingly diflicult, were fii'st 

 described by Messrs. Sollitt and Harrison, who estimated them at 

 from 120,000 to 130,000 to the inch. Their estimate has been 

 adopted by the ' Micrographic Dictionary ' and by the majority of 

 modern writers who have referred to this test ; but so many difficul- 

 ties beset the resolution that few microscopists appear to have 

 attempted to verify the original estimates. Indeed, most observers 

 would seem to have been unsuccessful in their efforts to resolve the 

 Amphipleura even with the best objectives, and some have gone so far 

 as to deny the existence of any strife ujion the frustules of this 

 species. Among the microscopists who claim to have seen the strife, 

 several would seem to differ from the original estimates of Sollitt and 

 Harrison as to their fineness. Dr. Eoyston-Pigott, whose papers on 

 " high-power definition" in the ' Monthly Microscopical Journal ' have 



