254 POPULAR SCIENCE MONTHLY. 



and reflections that are green, and if we do not see tliem habitually 

 it is because we do not give sufficient attention to them. 



A common division of the spectrum is into warm and cold colors. 

 The warm colors are red, yellow, orange, and yellow-green; the 

 cold colors are violet, blue, green, and blue-green. This is not an 

 arbitrary division, but answers to a fact of experience which passes 

 from our physical to our moral impressions, and may cause in us 

 feelings of comfort or uneasiness, joy, sadness, or moral depression. 

 Some persons are influenced by the gray-colored sky, others are gay 

 when the day is bright. It is a current expression that the color of 

 the southern landscape is warm. Goethe said that blue caused him 

 to feel cold. 



The terms warm and cold are technical expressions in the arts. 

 A color tone is cooled by putting blue in it, and warmed by adding 

 red or yellow. " This practice is not arbitrary," says M. F. Bracque- 

 mond in his book on Design and Color ; " it copies the colored aspects 

 which natural light imposes on all imitation that seeks to realize the 

 colored and factitious light of painting. To reach this, art observes 

 the order according to which the natural lights distribute their vari- 

 ous colored elements, and classes luminous aspects — a process which 

 it has always observed — into the two categories of warm and cold. 

 Hence, so far as examples come to us, this contrast is easy to verify; 

 at the Louvre, for example, in works from Pompeii, and in those of 

 all the masters." Preyer relies upon this division of colors into 

 warm and cold for a comparison of chromatic sensations with thermic, 

 and for supposing that the color sense is developed from the sense 

 of temperature. Chromatic sensitiveness to this author is only a 

 special case of thermic sensitiveness limited to the retina. Darwin's 

 ideas were evidently the same; the whole human body was a sort 

 of retina capable of improvement; we may, it is true, suppose with 

 Lord Kelvin that " there is absolute continuity between the percep- 

 tion of heat by the retina of the eye and its perception by means 

 of the tissues and nerves." 



A very elementary experiment will easih' enable us to recognize 

 these different qualities of colors. Set a lighted candle on a table 

 near a window; there are then two sources of light — the daylight, 

 blue and cold, and the light of the candle, orange-red and warm. 

 Cast a shadow on the white paper by holding a pencil straight up. 

 The shadows cast by the candle will be blue to a degree that no one 

 can mistake it, a greenish blue. Placing the pencil between the 

 window and the candle and looking at the shadows, we have, first, 

 the blue shadow of the candle, and then the shadow projected by 

 the cold daylight. The color of the last, though perhaps less evident 

 than the other, is an orange-yellow, of rich, warm tone. 



