^^ [Feb. 21, 



aud some quartz plates with parallel sides. These all seemed to be 

 rather opaque, though I think the exposure was probably too short. 

 We shall experiment in this line at another time. 



The second slide shows the skeleton of a lady's hand, which, as far 

 as I know, is the first that has been produced. 



The third slide illustrates the difference in the density of the nega- 

 tive caused by times of exposure on the four quarters of the plate of five, 

 ten, twenty, forty -five minutes respectively. During the exposure of 

 each quarter, the rest of the plate was protected by metallic screens. 

 The test objects on the plate, are : a circular piece of cork ; a gold coin ; 

 a strip of magnesium tape ; a piece of glass, and a piece of aluminum. 

 The distance of the tube from the plate was about ten and a half centi- 

 meters during all four exposures. 



The fourth slide shows the skeleton of a mouse, taken laid flat upon 

 its back ; the legs being stretched out and brought as near the plate as 

 possible. 



Slide No. 5 shows the density of the negative produced by five- 

 minute exposures, at distances of two and a half centimeters, five cen- 

 timeters, seven aud a half centimeters, ten centimeters aud twelve and 

 a half centimeters respectively. The plate was protected by a screen 

 of copper having a circular aperture about one centimeter in diameter. 



Slides No. 6 and 7 show the density produced at a distance of two and 

 a half centimeters, with exposures of one to five minutes. These slides 

 were also prepared to demonstrate the efficiency of a plate especially 

 sensitized by Mr. John Carbuttof this city for this work. He conceived 

 the idea that the photographic plate might be rendered more sensitive 

 to this energy, if the film were treated with some fluorescent substance. 

 Mr. Carbutt very kindly placed in our hands some of the special 

 plates, and your attention is directed to a comparison between a very 

 rapid ordinary plate (Seed's No. 27), and the one especially prepared. 

 The treatment throughout was precisely the same. The prepared plate 

 seems to have been considerably more sensitive than the other. 



Slides Nos. 8 and 9 show the results of tests to demonstrate the pos- 

 sibility of reflection or refraction, by means of two large diamonds set 

 in a ring. First the diamond ring was enclosed in a flat purse with 

 some coins, and certainly the result is very interesting, though, per- 

 haps, it would be premature to say that anything new is proved by it. 

 The ring was next placed open directly upon the covered plate, aud ex- 

 posed in two positions. 



Slide No. 10 shows a possible application of the Riintgen process. 

 "Wishing to test the value of the method for detecting flaws in metals, 

 the writer requested one of his associates. Dr. Richards, to have pre- 

 pared three aluminum plates, four or five millimeters thick, with hidden 

 holes, plugs, or any flaws that might seem desirable. Dr. Richards was 

 asked further to prepare a detailed description of the plates, to sign and 

 seal it, and to bring it with him this evening. The aluminum plates 



