Chapter X: TECHNOLOGY.--Cotton Seed Oil.--How cotton seed oil is (5)

1. In reading, a book or newspaper should be held at a distance of from ten to fifteen inches from the eyes. It is hardly necessary to caution anybody not to hold the print further away than fifteen inches. The only objection to holding ordinary print too far away is that in so doing the pictures formed on the back wall of the eye are too small to be readily and easily perceived, and the close attention consequently necessary causes both the eyes and the brain to tire. Most persons quickly find this out themselves, and the tendency is rather to hold the book too near, for the nearer the object to the eye, the larger its picture upon the retina, or back eye wall. But here we encounter another danger. The nearer the object the eyes are concentrated upon, the greater the muscular effort necessary; so that by holding the book too near, the labor of reading is greatly increased, and the long persistence in such a habit is likely to produce weak eyes, and may, in some instances, lead to real near-sightedness. When children are observed to have acquired this habit and cannot be persuaded out of it, they should always be taken to a physician skilled in the treatment of the eye for examination and advice. A little attention at such a time may save them from a whole lifetime of trouble with their eyes. Of course, the larger the print, the farther it may be held from the eyes.

POSITION.

2. The position of the person with regard to the light should be so that the latter will fall upon the page he is reading, and not upon his eyes. It is generally considered most convenient to have the light shine over the left shoulder, so that in turning the leaves of the book, the shadow of the hand upon the page is avoided. It is not always possible to do this, however, and, at the same time, to get plenty of light upon the page. When one finds himself compelled to face the light in reading, or in standing at a desk bookkeeping, he should always contrive to shade his eyes from a direct light. This may be done with a large eye shade projecting from the brow. A friend of mine, a physician, is very fond of reading by a kerosene lamp, the lamp being placed on a table by his side, and the direct light kept from his eyes by means of a piece of cardboard stuck up by the lamp chimney.

PROPER LIGHT.

3. The illumination should always be sufficient. Nothing is more injurious to the eyes than reading by a poor light. Many persons strain their eyes by reading on into the twilight as long as they possibly can. They become interested and do not like to leave off. Some read in the evening at too great a distance from the source of light, forgetting that the quantity of light diminishes as the square of the distance from the source of light increases. Thus, at four feet, one gets only one-sixteenth part of the light upon his page that he would at one foot. It is the duty of parents and others who have charge of children to see to it that they do not injure their eyes by reading by insufficient light, either daylight or artificial light. There is a common notion that electric light is bad for the eyes. The only foundation I can think of for such a notion is that it is trying to the eyes to gaze directly at the bright electric light. It is bad to gaze long at any source of light, and the brighter the source of light gazed at, the worse for the eyes, the sun being the worst of all. I have seen more than one person whose eyes were permanently injured by gazing at the sun, during an eclipse or otherwise. As a matter of fact, nothing short of sunlight is better than the incandescent electric light to read by or to work by.

READING IN BED.

As to reading while lying down in bed or on a lounge, I can see no objection to it so far as the eyes are concerned, provided the book is held in such a position that the eyes do not have to be rolled down too far. Unless the head is raised very high by pillows, however, it will be found very fatiguing to hold the book high enough, not to mention the danger of falling asleep, and of upsetting the lamp or candle, and thus setting the bed on fire. Many persons permanently weaken their eyes by reading to pass away the tedious hours during recovery from severe illness. The muscles of the eyes partake of the general weakness and are easily overtaxed. Persons in this condition may be read to, but should avoid the active use of their own eyes.

READING IN RAIL CARS.

Reading while in the rail cars or in omnibuses is to be avoided. The rapid shaking, trembling or oscillating motion of the cars makes it very difficult to keep the eyes fixed upon the words, and is very tiresome. I have seen many persons who attributed the failure of their eyes to the daily habit of reading while riding to and from the city. Children should be cautioned against reading with the head inclined forward. The stooping position encourages a rush of blood to the head, and consequently the eyes become congested, and the foundations for near-sightedness are laid.

(_To be continued._)

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TESTING INDIGO DYES.

The author deals with the question whether a sample of goods is dyed with indigo alone or with a mixture of indigo and other blue coloring matters. His method may be summarized as follows: Threads of the material in question should give up no coloring matter to boiling water. Alcohol at 50 and at 95 per cent. (by volume) ought to extract no color, even if gently warmed (not boiled). Solution of oxalic acid saturated in the cold, solution of borax, solution of alum at 10 per cent., and solution of ammonium molybdate at 33-1/3 per cent. ought not to extract any coloring matter at a boiling heat. The borax extract, if subsequently treated with hydrochloric acid, should not turn red, nor become blue on the further addition of ferric chloride. Solutions of stannous chloride and ferric chloride with the aid of heat ought entirely to destroy the blue coloring matter. Glacial acetic acid on repeated boiling should entirely dissolve the coloring matter. If the acetic extracts are mixed with two volumes of ether and water is added, so as to separate out the ether, the water should appear as a slightly blue solution, the main bulk of the indigo remaining in suspension at the surface of contact of the ethereal and watery stratum. This acid watery stratum should be colorless, and should not assume any color if a little strong hydrochloric acid is allowed to fall into it through the ether. No sulphureted hydrogen should be evolved on boiling the yarn or cloth in strong hydrochloric acid. On prolonged boiling, supersaturation with strong potassa in excess, heating and adding a few drops of chloroform, no isonitrile should be formed.--_W. Lenz_.

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TRANSCRIBER'S NOTES

1. Simple and obvious typographical errors have been corrected.

2. In the article "Manufacture of Photosensitive Plates", the original
text referred to room U twice. The first instance has been changed
to room T.

3. In the article "An Improved Screw Propeller", the text refers to the
propeller in figure A as being four bladed and also two bladed. It
is clearly two bladed and the reference to it being four-bladed has
been corrected.