Page:Popular Science Monthly Volume 7.djvu/521

Rh tropical America. It has a straight stem, eight or ten feet in height, and produces yellow flowers like those of the sunflower, but smaller. The thick, fleshy, perennial root produces a large number of tubers, in appearance not unlike potatoes. These are not as nourishing as potatoes, but, when properly prepared, are very palatable food, and make a very good soup. It is usually propagated by small tubers or by cuttings, like the potato.

Toughened Glass.—A process for increasing the cohesive power of glass has been invented by a French engineer, François de la Bastie. This process consists in heating the glass to a certain temperature and plunging it while hot into a heated oleaginous compound. The time occupied in the actual process of tempering is merely nominal, for directly on being heated to the requisite degree, the articles are plunged into the bath and instantly withdrawn. The toughened glass cannot be cut by the diamond, and hence when it is used for windows it must be cut to the proper size before it is tempered. Articles of this toughened glass, such as watch-crystals, plates, dishes, and sheet-glass, were recently exhibited in London, and experiments made to show wherein this material differs from common glass. Water was boiled in a saucer over a fire, and the saucer quickly removed to a comparatively cold place; it was unaffected by the sudden change of temperature. One corner of a piece of glass was held by the hand in a gas-flame until the corner became exceedingly hot, but the heat was not communicated to the other portion of the glass, nor was it cracked from unequal expansion.

The following experiment was then made to show how this toughened glass compared with common glass in power of resistance to fracture by the impact of a falling weight. The two pieces of glass to be tested were each about six inches square, and placed in frames, the weight being dropped upon the centre. With the ordinary glass, a two-ounce brass weight, falling on it from a height of twelve and eighteen inches respectively, did no damage, but at twenty-four inches the glass was broken into fragments. With a thinner piece of the toughened glass no impression was made by the same weight falling from heights ranging from two to ten feet, the weight simply rebounding from the glass. An eight-ounce iron weight, tried at two to four feet respectively, gave similar results. The height being increased to six feet, the glass broke.

Some of the public prints have ascribed to Bastie's tempered glass properties which the inventor himself has never claimed for it. Thus it has been qualified as malleaablemalleable [sic] and "unbreakable." But Mr. Thomas Gaffield, of Boston, a perfectly competent judge, who has examined specimens of this tempered glass, thinks that the true value of this invention is by no means determined as yet. He perceives in it sundry qualities which detract from its usefulness. First, as we have stated, it cannot be cut by the diamond. Then, on being subjected to the sand-blast, it flies into small fragments. Many of the specimens seen by Mr. Gaffield were not transparent, but only translucent. In ordinary window-glass, if a large pane be broken, the fragments may be cut into smaller panes, but with the De la Bastie glass such economy is out of the question. From the fact that this improved glass, though before the public for a whole year, has not yet found a place in commerce, Mr. Gaffield is inclined to suspect that the invention is for some reason impracticable.

Can Birds converse?—Dr. Charles C. Abbott cites the following occurrence to show that birds possess some mode of conveying ideas to one another. In the spring of 1872 a pair of cat-birds were noticed carrying materials for a nest to a patch of blackberry-briers hard by. To test their ingenuity, Dr. Abbott took a long, narrow strip of muslin, too long for one bird conveniently to carry, and placed it on the ground in such a position as to be seen by the birds when searching for material. In a few moments, one of the cat-birds spied the strip and endeavored to carry it off; but its length and weight, however he took hold of it—and he tried many times—impeded his flight, and, after long worrying over it, the bird flew off for assistance. In a few moments he returned with his mate, and then, standing rear the strip, they