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 uncomfortable, 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 necessary 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 contrast; as the illumination increases the contrast becomes better and reading 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 illumination the greater the ease of reading. Hold the page directly in the sunlight; can you read it easier? There is a certain amount of illumination 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 particular 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 "midnight" 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 illuminated, and lighted just to the point of maximum comfort, all other objects 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.