354 THE POPULAR SCIENCE MONTHLY. 



WINDOW LIGHTS AND THEIR VALUE. 



BT JAMES L. GEEENLEAF, 



ADJUNCT PROFESSOB OF CIVIL ENGINEEBING IN COLUMBIA COLLEGE. 



MOST subjects of analysis can be studied both in quantity and 

 quality, and light is no exception to the rule. Color as a 

 quality of light has always been a popular study. A vast deal 

 of experiment and attention has been given to the harmonics 

 of color, and many who make no claim to scientific attainment 

 are well versed in it. Every child knows the colors, but the ex- 

 pression " quantity of daylight " has a strangeness and a vague- 

 ness about it that are not felt by children only. This is largely 

 because there is such a wealth of daylight about us. "Silver 

 was nothing accounted of in the days of Solomon." Light is 

 not measured, because it is lavished upon us by an unstinting 

 hand. But light can be measured. Although intangible, it has 

 quantity quantity of effect, if it may be so expressed. If this 

 seems fanciful, it may be remarked that there is nothing fanciful 

 about the measurement of heat, and yet the case is quite analo- 

 gous. The thermometer is simply a contrivance for measuring 

 variation of intensity in heat. Quantities of heat effect are con- 

 tinually being estimated, for economy in its use is of prime im- 

 portance. Light, on the contrary, is ready at hand. Ordinarily 

 objects are flooded with a brilliancy of daylight which is as free 

 as air. There can scarcely be need of economy with light when 

 the world is floating in it. But there is nothing impossible in its 

 measurement. Possibly, if the sun were less prodigal in pouring 

 out his rays upon the earth the measurement of daylight would 

 be a more common operation than at present. Every means 

 would be taken to utilize it without waste. We would see the 

 owners of buildings making careful estimates of the light belong- 

 ing to their properties even dividing it into lots and renting 

 them separately. At the least, we would see them more jealously 

 than now defending their light from obstructions built around 

 them. 



Windows are the natural and all-important resource of the 

 architect. All the light which enters the building must pass 

 through them. It is a very patent fact that the larger they are, 

 and the more numerous, the greater the total amount of light 

 which enters. It is not as widely appreciated, however, that there 

 are other conditions affecting the amount and quality of the enter- 

 ing light that are sometimes ruling in their effect. 



Looking from a window, one sees a variety of surfaces sees 

 them because of their reflecting different intensities and colors of 

 light. If asked to classify them according to relative reflecting 



