362 THE POPULAR SCIENCE MONTHLY. 



matter of any concern, because a slight difference in hue from 

 their appearance under pure white light does not materially affect 

 our appreciation of most objects. There are, however, special 

 operations which are thus affected to an extent that is of practical 

 importance. A conversation with a cotton broker, for example, 

 will do much to increase respect for the sensitiveness of the 

 trained eye, and convince one of the practical bearing of these mat- 

 ters. Careful observation is needed to judge cotton and grade 

 different samples, and the eye becomes wonderfully skilled in 

 doing so. A steady, clear sky light is desirable. Evidence is at 

 hand of the injurious change upon the light caused by alterations 

 in buildings across the street from a cotton sample room. In the 

 course of building operations in Pearl Street, New York city, a 

 dull, buff-colored wall was taken down and replaced by red brick. 

 The result when the sun shone upon the surface was a noticeable 

 and injurious change in the light that came into the windows. A 

 flush of pink was cast over the cotton samples, perhaps too slight 

 to be noticed ordinarily, and yet giving a tone to them which 

 interfered with the judgment of their quality. 



And now a few words in conclusion concerning the service the 

 light performs when it finally reaches the room. That light which 

 passes directly from the window to the eye is of no benefit, except 

 as it enables one to see the outside view. Nearly all the light 

 serves a far more useful purpose. It enters the window and sets 

 in operation on a smaller scale the same phenomena that are tak- 

 ing place in the street. It is bandied back and forth between 

 walls, carpet, furniture, and occupants. The light that these vari- 

 ous surfaces reflect gives impressions of form and color by which 

 we appreciate objects. By means of it we see our friends' faces, 

 enjoy the pictures, read the book. It should be noted that light 

 and color are entirely subjective. They are effects produced in 

 the brain by different kinds of light undulations. We perceive 

 the color of the upholstery and carpet because these have the 

 faculty of sorting out undulations of special wave lengths and 

 reflecting them. We perceive the outline of chair or of face partly 

 by change of color, but chiefly by light and shade, the difference 

 in intensity of the undulations coming from them and from ob- 

 jects behind them. To make the objects in the room distinct the 

 light entering the windows must be conserved as much as pos- 

 sible. This will best be accomplished by banishing all dark ma- 

 terials. Heavy hangings absorb light as well as dirt. Oak or 

 enameled furniture reflects the light that black walnut or rose- 

 wood absorbs, and a light-colored wall will do almost as much as 

 a sunny disposition to fill a room with sunshine and good cheer. 



