1 96 THE POPULAR SCIENCE MONTHLY 



shade over the light, enamel-white inside, is the best. A white shade 

 lights up the room in general too much, and necessitates the student 

 wearing a green eye-shade on his " noble brow." The latter is uncom- 

 fortable, and quite unnecessary if put over the light instead of over 

 his eyes. 



Third, a student oil-lamp gives the most satisfactory illumination, 

 if kept in good order. The wick should be kept free from excrescences, 

 so that it always gives its proper, steady, mellow, yellow light. The 

 ordinary gas burner nickers too much, the electric light is steadier but 

 can not be regulated, the Welsbach-mantle light is too brilliant if turned 

 on full and too variable if turned down. 



Fourth — and most important of all — turn the light down low, and 

 then turn it down some more ! Given the right kind of light, the student 

 lamp, one third to one half its full illuminating power, is all that is neces- 

 sary or desirable. The reason is highly important, for reading easily and 

 for the welfare of the eyes, and it is this : We see the print by contrast of 

 nearly black against nearly white ; with no illumination there is no con- 

 trast ; as the illumination increases the contrast becomes better and read- 

 ing is easier. At a certain point, the contrast is greatest and reading is 

 easiest. But it is an entirely erroneous idea that the greater the illumina- 

 tion the greater the ease of reading. Hold the page directly in the 

 sunlight ; can you read it easier ? There is a certain amount of illumi- 

 nation at which the contrast of print against paper is a maximum and 

 where reading is easiest, with least fatigue to the eyes. This point 

 varies for different-sized prints, for different inks, for differently 

 surfaced papers and for different tints of papers. The point can be 

 readily and easily determined in a fraction of a minute, in any particu- 

 lar case, by any one wishing to find it, by simply turning the light 

 slowly up, keeping the eyes on the book, and noting the least light at 

 which the print is clearly seen and read without sensible effort. This 

 is the point at which you can read that book the longest without strain 

 or fatigue; it will usually be found at about one half or less of the 

 illumination ordinarily used. (I will not speak of the saving in "mid- 

 night" oil thereby attained; the saving in "eyes" is more important.) 

 One can often read and study for hours with this light, whereas a 

 brighter light would really make reading more difficult and tire out the 

 eyes in a fraction of the time. 



The effect of heeding and using the above principle is that eye- 

 fatigue is minimized and thus study is done with less distraction from 

 this cause. The point explained is the point of maximum comfort, 

 and, therefore, of maximum efficiency. With only the book illumi- 

 nated, and lighted just to the point of maximum comfort, all other ob- 

 jects in the room in semi-darkness, and the student anxious to study, 

 let us leave him to himself, to see what he can make out of the situation. 



