Page:Popular Science Monthly Volume 1.djvu/781

Rh nearer to the eye than ten inches at least. Besides this, the book ought to be raised 20° for writing, and about 40° for reading.

Ordinarily, minor considerations, such as the most compact disposition of the seats, or placing the pupils so that the teacher may the most readily look into their faces, govern the arrangements of the class-room, and, when any attention is paid to the matter of light, it is often to the detriment rather than the benefit of the class. For example: one of the rules laid down by the Educational Department in London, for the guidance of architects, is, that "the windows should be so placed that a full light should fall upon the faces both of the teachers and the children." Light coming from the right hand is not so good as that from the left, because the shadow of the hand falls upon that part of the paper at which we are looking. Light from behind is still worse, because the head and upper part of the body throw a shadow on the book or paper; but the light that comes from the front, and falls on the face, is by far the worst of all; for it not only defeats the object desired—illuminating the faces of the children—but is most hurtful to the eye. Instinctively desirous of avoiding the unpleasantness of the full glare, the children will assume all sorts of positions, which turn their faces from the master. In reading, they turn the head round the vertical axis, generally toward the right, in order to let the light fall on the book, which, when held straight before them, is completely in shadow; while, in writing or reading (the book being on the table), they bend their heads as low as possible, in order to shade their eyes by the projection of the forehead.

The best light for the school-room is from above; but, when this cannot be obtained, the desks should be so arranged, in connection with the windows, that the light shall fall upon the book or paper from the left.

Where light from gas or other artificial source is used for evening work, it should be made as steady as possible, and the lights so placed that they will not come opposite the eye, as in this situation they are dazzling and injurious. Ground-glass globes ought not to be used, for, though valuable in an ordinary room, where they tend to diffuse the light more equally, they give an indistinct light for work, and thus put a greater strain upon the eye. And, for the same reason, ground or ribbed glass should not be employed for the lower portions of windows, as the optical effect of such glass in that position is decidedly hurtful.

Jute.—This remarkable fibre, which formerly was only used for the coarsest purposes, has of late become invaluable. It makes a serviceable substitute for hair in chignons, and is now used extensively as a "mix" in silk. Owing to its kindly way of taking the dye, and the gloss which it sustains, a large quantity can be used in silk, and yet defy detection, except by an expert. It is, in consequence, highly desirable that it should be produced in our country, if possible. Some experiments by agriculturists are under way, which seem to promise success. Mr. F. T. D. Lacroix, of New Iberia County, Louisiana, has, on his plantation, several rows of the jute-plant, the seed of which was sent to him by the Department of Agriculture. The plants are very vigorous, and the indications are that jute will thrive in that climate. It bears some resemblance to flax in appearance, as it is said to in fibre.

A City's Waste.—Mr. Lepmann, director of the Central Trial Station, in Bavaria, speaks thus of the loss of fertilizers in Munich, a city of 177,000 inhabitants. He makes the sum of fertilizing elements wasted in the human excrements of the city for one year, 1, 857,714 pounds of nitrogen, of which the commercial value is 866,934 gulden; 611,054 pounds of phosphoric acid, value 122,210 gulden; 372,375 pounds of potash, value 49,650 gulden; total value 1,038,794 gulden, equal to about $500,000. This sum would be still further increased by adding to it the value of the humus-forming constituents of the excrements wasted. To make up for that waste, he states that the amount of guano furnished by Peru yearly for the German fields is about 1,000,000 cwt.

Mr. Lepmann states that Germany now possesses a system by which he is confident this enormous waste may be entirely prevented, called there the Tonnen (barrel)