Page:Popular Science Monthly Volume 7.djvu/266

254, and soon the microscope showed some of the rotifers to have revived, while others remained motionless. The same slides were again submitted to drying, the cover-glass of one having been removed. Several hours after moistening them, the next day, only two rotifers were seen to be alive on each slide. Again some twenty active rotifers were exposed to the hot sun during the afternoon. These could not be revived the following morning. From all this it would appear that rotifers become inactive in comparatively dry positions, and may be revived by supplying moisture; but, when their own substance is actually dried up, it is impossible to revive them.

Influence of Ammonia on the Color of Flowers.—Exposure to the smoke of a cigar changes violet-colored flowers to green. This change is due to the ammonia present in tobacco-smoke. The general question of the influence of ammonia on the colors of flowers has been lately investigated by Gabba, an Italian, his method being to put a little ammoniacal solution in a basin, and place a receiver over it containing the flower. In this way blue, violet, and purple flowers were changed to green, carmine-red flowers to black, white to yellow, etc. The most singular changes were presented by flowers in which several tints are combined; the red lines changed to green, the white to yellow, and so on. After the flowers have undergone these changes, if they are placed in pure water, they retain their new coloration several hours, and then gradually resume their original hues. Gabba has further observed that the flowers of aster, which are naturally inodorous, acquire an agreeable aromatic odor under the influence of ammonia. When moistened with dilute nitric acid they change from violet to red. If inclosed in a wooden case, and exposed to hydrochloric-acid vapor, they in six hours assume a beautiful carmine red.

Metal Roofs as Lightning-Conductors.—In a communication to the French Academy of Sciences, E. Nouel gives the results of his observations, made at Vendôme during a very violent storm. The lightning on that occasion struck some telegraph-posts and three houses. In the case of the houses, Nouel found that the lightning followed the sheet-zinc roofing (without damage) to the spouts, and thence to the earth. The author remarks that static electricity flows always to the surface of bodies, so that a gutter and its pipe, notwithstanding the thinness of the metal, constitute an excellent electric conductor, having less resistance than the best lightning-rods; that the thunder-bolt, as a rule, falls only during heavy showers, by taking advantage of the semi-communication with the earth offered by the vertical series of rain-drops. The summary of his conclusions is as follows: 1. It is possible, almost without expense, to protect ordinary houses from lightning casualties by establishing good metallic communication between the chimney-flues and roof, through the gutters, and by trusting to the rain to complete the communication to the ground. 2. That, even for complete lightning-conductors, we should utilize as a conductor the gutters and their pipings. 3. That there is need in every case to wholly replace the conductors of lightning-rods with hollow pipes of the same mass and of greater diameter. He decidedly rejects metallic cords, because electricity, always following the conductor's surface, only selects or uses from this cord a small number of its wires, which may be easily fused.

A Botanic Garden for Chicago.—The Commissioners of the South Park, Chicago, have in contemplation the establishment of a Botanic Garden on the following liberal plan: First, there will be a botanic garden proper, in which all indigenous plants of the United States, and hardy species from other countries, will be arranged, as far as possible, according to their natural affinities, while hot-houses and green-houses will be provided for the reception and display of tropical plants. There will also be an arboretum, or collection of hardy trees, from all parts of the world, planted in such order as to serve the purposes of science and ornament; a garden devoted to floriculture; a botanical museum, for the exhibition of vegetable economic products; an herbarium, or collection of specimens of dried plants, scientifically arranged; finally, a library of botanical works. The South Park comprises about 1,200 acres, and the