Proceedings of the Polytechnic Association. 901 



tlie red and violet, toward the end, are tlie least so. To the question 

 why the setting sun looks red is answered that, by the law of 

 refrangibility of the different colors contained in white light, the 

 least refrangible rays, which are the red and orange, in a great depth of 

 any colorless refracting medium, penetrate best in a straight direc- 

 ti(^n. The more refrangible rays, the violet, blue and green, have a 

 stronger tendency to sideway refraction, and this is the simple reason 

 of the bright blue color of the sky and the dark blue color of water, 

 if pure and of great depth. Divers, when under water, also see the 

 sun red for this reason. 



An'other item on "Reflected Sunlight in Photography " elicited 

 the following remarks from Dr. Vanderweyde : Photographs are 

 taken in this city by reflected light, that is, a non-inverted ambro- 

 types and ferrotypes by means of a small mirror or reflecting glass 

 prism attached to the front lens of the camera. Mr. Kurtz, photo- 

 grapher of this city, has produced what is called Rembrandt eftects 

 by means of light reflected by white surfaces. He, the doctor, had 

 lately traveled a distance of thirty -six miles in the mammoth cave in 

 Kentucky, and had some fine photographs which were taken there 

 by the magnesium light. 



Mr. S. Beer said he had taken very good photographs of basements 

 and cellars by the magnesium light. 



Reflected Sunlight in Photography. 

 Dr. H, A^ogel, the German correspondent of The Philadelphia 

 Photographer, after alluding to a new photographic light lately used 

 in Yienna, which consists of oxyd of titanium, heated by a hydro- 

 oxygen flame, says, he has lost much confidence in all artificial lights. 

 His experience in the Egyptian tombs was the cause of it. In many 

 of them he had burned large quantities of magnesium wire without 

 arriving at any satisfactory result, and succeeded, finally, much better 

 with reflected sunlight. An opening was made in a funeral vault ; 

 the rays of sunlight were caught by a mirror and thrown on the 

 object. The effect was better than fifty feet of magnesium wire. By 

 moving the mirror the light glides over the object, and in this way, 

 lie had copied wall-painting, dark corners, ceilings, etc. His example 

 has been iniitated. The photographer, Hammerschmidt, has recently 

 taken the interior of the Church of the Hoh' Sepulchre, at Jerusalem ; 

 also, the Anointment Stone of Christ, in the same church, bj means 

 of reflected light He has succeeded admirably where all former 



