2 JOURNAL OF THE [January, 



when fed by a suitable battery, was better by far than any he 

 had previously employed ; also that an electro-motive force of 

 six or seven volts amply suffices for all uses. 



The views of Dr. Van Heurck are ably seconded by Dr. Theo- 

 dor Stein, of Frankfort-on-the-Main, in an article contributed 

 by him to the " Zeitschrift fiir Wissenschaftliche Mikroskopie," 

 Vol. I., No. 2 (1884). I have made a digest of such parts as 

 are material to my purpose, as follows. 



'The electric light,' says Dr. Stein, 'has been in use many 

 years for showing microscopic objects by projection upon a 

 screen with the use of the magic lantern. With constant im- 

 provement in the. manufacture of objectives, the discernment of 

 fine structure was possible even by this method. But the excel- 

 lence of the performance found its limit at a power of eighty 

 diameters, a higher amplification seriously impairing definition. 



' At the Electrical Exhibition in Munich, in 1882, trial was 

 made of the advantage of electrical illumination in working with 

 the compound microscope. The light furnished was found to 

 be sufficient for the finest observation with objectives of the 

 highest power, and to be free from the well-known disadvantages 

 of other kinds of artificial light; — the yellow ray and the heat 

 ray. All possible preparations were examined, such as muscle, 

 nerve, epithelia, bone, skin, bacteria, diatoms, &c. Especially 

 surprising was the faultless picture of the red blood-corpuscles, 

 to the correct showing of which a yellow light is ])articularly 

 inimical. In the region of blue and violet, the spectrum of the 

 light from an incandescence lamp is incomparably more intense 

 than that of light from any other artificial source. In these ob- 

 servations light of different intensities was used, ranging between 

 sixteen and sixty candle-power, and was received by the sub- 

 stage mirror and was reflected thence upon the object. 



'These experiments suggested to me, in the winter of 1882, 

 the idea of setting aside the mirror, and placing the incandes- 

 cence lamp beneath the stage for the direct illumination of the 

 object. As no lamp small enough for the purpose was in exist- 

 ence, I requested Mr. C. H. F. Miiller, of Hamburg, to make 

 me some according to certain specifications which I gave him. 

 At this time appeared in the Journal of the Royal Microscopical 

 Society^ an article by C. H. Stearn, who, at a meeting of the 



»Cf. Journ. R. Blicros. Soc, Ser. II., Vol. III., 1883, Pt. 1, p. 29. 



