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III. — On the use of Incandescence Lamps as Accessories to the 

 Microscope. By C. H. Steaen, F.R.M.S. 



{Bead 10th Jamiary, 1883.) 



As for the last ten years I have not followed the progress of micro- 

 scopical science, I cannot but feel that in venturing now to speak 

 on microscopical subjects, I am in a similar position to that of a 

 colonist who, on retui-ning to his native land, finds that the world 

 has moved on and left him far behind. Yet it is my hope that 

 from those fields of research in which my thoughts have of late 

 years been straying, and in which my former microscopical pursuits 

 have been discontinued, I may have been able to glean some infor- 

 mation which, though not primarily connected with microscopical 

 science, may, in its practical application, prove of some utility to 

 microscopists. 



When, in 1871, I first commenced the study of the physics of 

 high vacua, it was with the object of investigating the law 

 governing the arrangement of the lines in the spectra of rarefied 

 gases ; but after my meeting with Mr. J. W. Swan, in 1877, I 

 entered with him upon an investigation, having for its object the 

 discovery of the conditions under which thin carbon conductors 

 could be rendered permanent when made incandescent by an 

 electric current in the most perfect attainable vacuum. With what 

 success that investigation was attended, my colleague has already 

 described in his lectures and pamphlets; and I presume that 

 there are few here present to whom its practical results in the form 

 of incandescence lamps are not by this time familiar. 



From a scientific investigation, the matter has now grown into 

 a great commercial enterprise, and ere many months are over, 

 there seems a probability that in many places gas will be entirely 

 superseded by electrical illumination. When this happy time 

 arrives, the application of the incandescence electric lamp to the 

 purposes of microscopical illumination will certainly become uni- 

 versal, as it will then be not only the purest and most satisfactory 

 light, but will be at the same time the most convenient. I hope, 

 however, to show that microscopists need not wait for the realization 

 of the hopes of the shareholders in electric companies, and the 

 fears of those interested in gas companies, but may at once discard 

 their troublesome oil or gas lamps, with many of their acces- 

 sories, and proceed at once to avail themselves of the advantages 

 of electric illumination. I am aware that Dr. Yan Heurck, of 

 Antwerp, has anticipated me in the apphcation of our lamps to the 

 Microscope ; but, as those employed by him were of comparatively 



