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of projection microscope, and also the lamp by which it was 

 illuminated. By means of drawings on the blackboard he 

 illustrated the combination of lenses used to secure the needful 

 corrections, and stated that with the electric lamp employed, a 

 source of light was obtained not exceeding half a square milli- 

 meter, which enabled him to show objects with perfect sharpness 

 and in a way never before accomplished, up to a magnification of 

 10,000 diameters. 



Mr. E. M. Nelson said Mr. Schroeder had pointed out very 

 clearly the necessity for illumination by a small point of light. 

 As regarded the magnification of 10,000 diameters, the light 

 became so greatly enfeebled that the object was practically 

 invisible to any one who was not close up to the screen. It would 

 be obvious that if the original source of light was equal to 10,000 

 candle power, and the image was magnified 10,000 times — to say 

 nothing of 10,000 diameters — they w^ould only get a light equal 

 to one candle-power on the screen. The lantern microscope would 

 always be found useful for showing objects to a small number of 

 persons round a small screen, but if they wanted to show the 

 object to a large number at a distance they must fall back upon 

 the lantern slide. Mr. Schroeder had shown them how to get a 

 great deal more light into an objective than they had been able 

 to before — but 10,000 diameters upon the screen was a thing 

 which he confessed he was rather doubtful about. 



Mr. Lewis Wright did not think it was easy for people who 

 had worked independently in matters of this sort to discuss them 

 on the spur of the moment. He had been able, as others had, to 

 do something in this direction himself, and was sure that all of 

 them had reached the same point as to the necessity of getting a 

 small and at the same time an intense light ; and if Mr. Schroeder 

 could give them a lamp such as he described, he would have done 

 a very great service to aU who were working with the projection 

 microscope. All the defects of the arc lamp which had been pointed 

 out were not, however, quite so bad as stated, bejcause when the 

 carbons were put in an inclined position they could in this way 

 get the top crater to the front and could use this as their source 

 of light ; but there was the flickering and shifting about of the 

 flame which proved so troublesome, so that if Mr. Schroeder was 

 able to get such a light as he had described it would be of great 

 service. It seemed, however, not to be strictly an arc, but was 



