44 



THE AMEIUCAI^ MONTHLY 



[March, 



and so disposed that, an object being 

 in the field of the microscope, to pho- 

 tograph it one has only to remove the 

 ocular, place the photographic appa- 

 ratus against the tube and make the 

 photograph. This arrangement served 

 very well, and it is thus that I made 

 my first good photographs of the beads 

 of the amphipleura. 



' Finally I constructed a still more 

 efficient device, which T have named 

 my automatic apparatus. This con- 

 sists of a ver}' small mahogany cam- 

 era, extremely light, receiving at its 

 posterior part a gelatino-bromide plate 

 of 4^ centimetres wide by 5^ in length. 

 Anteriorly the camera carries a cop- 

 per tube 5^ cm. in length terminated 

 by an amplifier of Zeiss, which is 

 much better than that of Tolles. The 

 copper tube enters the tube of the 

 microscope a short distance. I call 

 this apparatus automatic because I 

 have nothing to do with it in any way. 

 It is so regulated that the object is 

 perfectly in focus with the No. i ocu- 

 lar of Powell & Lealand and also on 

 the sensitive plate. 



' This eflect is, naturally, only ob- 

 tained with certain objectives. As it 

 is, my apparatus works admirably 

 with the jij and the ^^-g homogeneous 

 objectives of Zeiss, and it gives with 

 the former a magnification of 300 and 

 with the latter of 450 diameters. For 

 considerably greater magnifications 

 one should make enlargements from 

 the plate, which offers less difficulty. 



' With this small apparatus I have 

 been able to photograph, without 

 trouble, very difficult things, for ex- 

 ample, diverse groups of Nobert's 

 test, including the 19th band.' 



Since writing the above we have 

 received a communication from Dr. 

 Van Heurck, which he has desired 

 us to publish. We do so with pleasure 

 in this connection. He writes as fol- 

 lows : 



' I have received No. 62 of the Am. 

 After. Journ. You certainly have the 

 right not to admit the photography of 

 the pearls of Amfhipleura pellucida 



before having seen the proof; but it 

 appears to me that you should, how- 

 ever, believe me sufficiently expert in 

 micrography and experienced instudy- 

 ing diatoms, to not presume that I 

 would take for beads illusory lines 

 which are easily seen upon Amphi- 

 pleura, but which are always parallel 

 to the margins of the valve. 



' I would only say that the striai 

 which I have photographed are abso- 

 lutely identical with those of Amphi- 

 pleura Lindheimeri, which I have 

 likewise photographed, and in all re- 

 spects analogous to those of Van 

 Heurckia rhomboides., a genus which 

 leads to Amphipleura by the variety 

 amphiplcuroides-grun.. of New Zea- 

 land. 



' I would add, finally ..that eminent 

 diatomists, such as Messrs. Cox and 

 Kitton, admit that there is not the 

 least doubt. Mr. Cox has written to 

 me that " There ought to be no ques- 

 tion as to the complete conclusiveness 

 of the evidence. It is as plain as in 

 the case of Van Heurckia rhom- 

 boides" Mr. Kitton says, " There 

 is no mistake, the granules are dis- 

 tinctly visible ; not that I ever doubted 

 their presence." Finally, Prof. Abbe 

 authorizes me to state that, in his 

 opinion, there is not the least reason 

 to doubt the reality of the pearls (re- 

 strictions made as to the real nature 

 of what diatomists have designated as 

 " pearls") ; that the structure is anal- 

 ogous \o that of many other diatoms, 

 and that my photographs clearly show 

 the typical image que doit donner, 

 avec nos microscopes actuels, une 

 structure periodique double (dans 

 deux directions plac^es a Tangle 

 droit) a intervalles si petite qu'il ne 

 peut pen^trer, dans le microscope, 

 au maximum, que trois des faisceaux 

 des plus interieurs que donne une 

 pareille structure.' 



We despair of rendering the latter 

 part of the concluding sentence in 

 good English, and therefore tran- 

 scribe the original French. The 

 question of the reality of the beaded 



