892 RECOBD OP CURRENT RESEARCHES, ETC. 



extent furnished empirical proof of the correctness of the deductions 

 of our theorists. 



Photographs of Pleurosigma angulatum, in which the polygons 

 ohsorved on the valves show as annular de2)ressions, have been 

 already published by Stein in his ' Das Licht im Dienste wissen- 

 schaftlicher Forschung ' (Leipzig, 1877), plate x. These photographs 

 were not, however, taken directly from the object, but were only en- 

 largements of a smaller microphotograph (reproduced from plate ix.) 

 made by photographic apparatus which enlarged it with a rather 

 objectionable effect, the original microphotograph exhibiting the 

 well-known hexagonal markings. 



To Mr. Carl Giinther, a photographer of Berlin, the credit is due 

 of having produced (exhibited at the recent International Fishery 

 Exhibition) two photographs of Pleurosigma angulatum taken direct 

 from the object, which as regards excellence of execution are at least 

 equal to the best productions of microphotography, and which at all 

 events are calculated to refute most thoroughly any objections which 

 may be urged against Stein's enlargements. 



Both photographs were taken by a dry process of J. D. Moller, 

 with direct sunlight and central illumination by Abbe's illuminating 

 apparatus, a concave lens being interposed. An old Guudlach's 

 immersion-system No. 7 was used, and with it one of the photographs 

 was produced with an amplification of 2000 times at the distance of 

 1 metre, and the other with an amplification of 5900 times at a 

 distance of 3 metres. 



In those places in which the photograph has come out perfectly 

 sharp (and consequently in the centre especially), both photographs 

 show, like Stein's enlargements, circular openings, with dark contour 

 and bright centre, a circumstance which characterizes them as being 

 without doubt " openings.''' 



Where the i3hotogra2:)hs are less sharp (near the margin, therefore) 

 the figures, which still produce the impression of oijenings, are more 

 angular, whereby on a superficial examination is produced the appear- 

 ance of the well-known " hatchings," running in three directions. 

 The larger photograjih shows, of course, these marked peculiarities 

 more clearly and strikingly than the smaller one. 



These photographs, it is certain, not only furnish a fresh proof of 

 the correctness of Abbe's theory of microscojiic vision ; but they 

 also plainly demonstrate the great importance of photography for the 

 study of the more difficult microscopical structures. 



New Microscopical Journal. — Herr Duncker, of Berlin, has com- 

 menced a 'Journal for Microscoj)ical Examination of Flesh and 

 Popular Microscopy ' (4to), which appears twice a month. The 

 thirteenth number, which is before us, contains articles on " Schools 

 for the Examination of Flesh," " Micrococci and Bacteria," " The 

 Collection and Preparing of Diatoms," &c. 



