IN NATURAL PHILOSOPHY. 37 



More of the light is transmitted, and less reflected. We see 

 this illustrated in greasing a bit of paper. It becomes semi- 

 transparent because more light passes through it, but looks 

 darker itself because less light is reflected to the eye. 



1 7. Does color exist in the object or in the mind of the ob- 

 server ? 



In the mind. Color in the object can be only a peculiar 

 property whereby a body absorbs some colors, and reflects or 

 transmits others. 



1 8. Why is lather opaque, while air and a solution of soap 

 are each transparent ? 



By repeated reflections and refractions in passing through 

 the unhomogeneous mass of lather, the rays are weakened. 

 The principle is the same as that of deadening floors with tan- 

 bark. (Phil., p. 161.) 



19. Why does it whiten molasses candy to pull it? 



Water is given up both in cooking and pulling. This causes 

 more light to be reflected (Q. 16), while the crystals formed, es- 

 pecially on the surface, hide the impurities. 



20. Why does plastering become lighter in color as it dries ? 

 Because, as the water evaporates, the mortar transmits less 



light, and reflects more light to the eye. . 



i 1 . Why does a photographer use a kerosene oil-lamp in the 

 "dark-ro'om?" 



Kerosene oil-flame emits only heat and color, but no actinic 

 rays. Some ' ' dark-rooms" are lighted with yellow glass windows. 



22. Is the common division of colors into "cold" and 

 "warm" verified in philosophy? 



Yes ; red contains more heat than violet. 



23. Why is the image on the camera, Fig. 167, inverted? 

 The rays cross each other at the focus of the double convex 



lens 



24. Why is the second image seen in the mirror, Fig. 134, 

 brighter than the firct? 



The first is formed by reflection from the glass, and the 

 second from the mercury. As the latter is a better reflector, 



