Photographical Section Proceedings. 1033 



Prof, Tillman believed that the vibratory wave of particles in 

 space was equal to the reflected light of the sun, plus the light or 

 effect from these particles. 



Prof. Vanderweyde stated that yellow glass would not obstruct 

 the actinic ray, if placed in direct sunlight. He attributed it to 

 the fact of the actinic ray being much more active, or not so easily 

 obstructed when accompanied by a great amount of the caloric ray. 

 He had composed a prismatic spectrum with colored glass, and 

 found that at noon, or when the greatest amount of caloric light 

 fell upon the prism, the yellow and other non-actim*c colors 

 admitted nearly as active printing force as the blue and purple. 



Mr. Hull had not met with any difficulty in working sensitized 

 plates upon which direct sunlight had fallen after x^assing through 

 the orange glass of his chemical room window, though the light 

 was first transmitted through a plain glass window, at some little 

 distance, and fell upon the orange glass at angles of about forty- 

 five degrees. 



Mr. Thomas had found, by careful experiment, that "flushed" 

 orange glass was much better for obstructing actinic light than pot- 

 metal glass, its efficiency being eight times greater. 



Prof. Vanderweyde explained the manufacture of the two kinds 

 of glass, saying, that as the best colors were very expensive, they 

 were used only as a thin coating upon one surface of the glass, 

 while the cheaper colors were mixed with the melted mass. 



Mr. Reed (a visitor) had used 3'ellow glass in direct sunlight 

 without experiencing any difficulty; but the light reached his 

 yellow glass after having passed thi'ough a plain window, as in the 

 case mentioned by Mr. Hull. 



Mr. Newton had prepared a good non-actinic glass by flowing 

 plain glass with a solution of iodine in ordinaiy negative varnish. 



Mr. Chapman had used a peculiar kind of tissue paj)er, and found 

 it to answer verj- well for obstructing the actinic light. 



Prof. Vanderweyde presented for examination a veiy fine 8x10 

 negative of Girard College, and explained the means by which it 

 was made. The lens used was an ordinary orthoscopic, behind 

 which combination he had placed a single achromatic plano-convex 

 lens, leaving between it and the back lens of the orthoscopic about 

 the same distance as that between the two lenses forming that 

 combination. He also gave an interesting account of experiments 

 which he had made with various combinations at Girard College, 

 and exhibited a print 10x12, made by a two-inch non-achromatic 



