PiXEMBtR 16, 1904.] 



845 



therefore, be visible to us if the length of the 

 multiple lies between 0.38 and 0.76. 



If, therefore, for botanical, physiological 

 and bacteriological work we stain our prepa- 

 rations with fluorescent substances and illu- 

 minate with ultra-violet light, we shall bring 

 into prominence smaller particles or struc- 

 tures than can possibly be seen with the 

 ordinary white or colored light. Or, if we 

 prefer, instead of the retina we may expose 

 a sensitized plate, especially one that is 

 sensitive to the particular fluorescent waves 

 excited by the special ultra-violet light that 

 we employ. 



But the success of this modification of the 

 ordinary methods depends also upon having 

 our microscope lenses so ground as to correct 

 for the particular waves that we are employ- 

 ing. In fact, one may conceive that an ultra- 

 violet wave of, for example, 0.09 microns may 

 by fluorescence excite a wave of 0.18, or 0.27, 

 or 0.36 microns, and will, therefore, still be 

 invisible to the eye, while perfectly competent 

 to do photographic work. It will, therefore, 

 be a great labor to grind the lenses properly, 

 since their perfection can only be tested by 

 experiments with invisible fluorescent rays; 

 but when perfected these lenses and the pho- 

 tographs give us a power of what we may at 

 present call ' ultra-microscope research.' The 

 development of such work is limited only by 

 the chemical and physical properties of atoms 

 and molecules, and is not in any way affected 

 by the limitations of the htmian eye. 



The first steps toward realizing this advance 

 in microscopy will naturally be made with the 

 ordinary microscope, and the ordinary soluble 

 fluorescent substances, among which we recall 

 cosine, thallene, quinine, sesculine, chlorophyll, 

 magdala red. If now with the fluorescent 

 staining and ultra-violet illumination we com- 

 bine the principles of the schleier method it 

 would seem that there will in the future be no 

 limit to the powers of research, except that 

 which is set by the diffraction phenomena. 

 The ultimate limit of actual photographic 

 visibility will be of the dimension of one or 

 two of the very shortest wave-lengths of ether, 

 or of the same dimensions as the larger mole- 

 . cules themselves. 



It is possible that Professor Ernst Abbe, of 

 Jena, and his colleagues have been working 

 along some line of thought similar to the 

 preceding, as I notice that in the list of scien- 

 tific instruments in the German educational 

 exhibit at the St. Louis Exposition, page 213, 

 mention is made of the ultra-microscopic 

 work, but from what little is stated it would 

 seem possible that this refers especially to the 

 ordinary microscope combined with the 

 schleier method; I have not as yet learned of 

 any details and may be entirely wrong. The 

 flood of ultra-violet light given out by the 

 soft-iron electrodes of Dr. Piffard's tube and 

 the magnificent fluorescent effects displayed 

 by Mr. Geo. F. Kunz in his lectures suggested 

 to me the preceding combination of fluores- 

 cence, the schleier method, and the micro- 

 photograph, and I have been encouraged to 

 publish the idea. 



To-day an interview with Dr. Sigfried Czap- 

 sky, a colleague of Professor Abbe's, has 

 brought to my attention the fact that great 

 improvements in ultra-microscope work are 

 in progress at Jena, but not yet sufficiently 

 developed to justify publication. I have, 

 therefore, taken the liberty of sending you 

 this communication in hopes that there will 

 be some suggestion in it worthy the attention 

 of these eminent opticians. 



Cleveland Abbe. 



Washington, 



November 6, 1904. 



EXTINCT PEDICULATE AND OTHER FISHES. 



While engaged on chapters relative to the 

 Pediculates for a work on fishes, I was ex- 

 tremely pleased to receive just what I wanted 

 — further information respecting the former 

 history of the order. I had received from Dr. 

 C. R. Eastman an interesting ' Bulletin of the 

 Museum of Comparative Zoology ' entitled 

 ' Descriptions of Bolca Fishes.' In that were 

 figures and description of a form referred to 

 ' LophiidcB ' and named Histionotophorus has- 

 sani (Zigno). A close examination of the 

 reproductions of photographic figures, how- 

 ever, convinced me that the fish was not one 

 of the lophiids but a typical antennariid. The 

 mode of fossilization showed that it was a com- 



