Page:Popular Science Monthly Volume 13.djvu/263

Rh ceased entirely. His arrival in the village, with the story of his adventure, created quite a sensation; but, when the bird was deposited on the ground to be examined at leisure, it revived for the third time, struck its claws through the hand of its captor, struggled to its feet, and would have escaped after all, if the enraged miner had not flung himself upon it, seized a stone and hammered its head to a jelly.

Muslin Glass.—The mode of producing so-called "muslin glass" is as follows: After carefully cleaning the surface of a plate of glass, a layer of verifiable color is laid over it, the vehicle being gum-water, and care being taken to have the pigment evenly applied. The glass is then submitted to a gentle heat until the water has evaporated, when a stencil of the desired pattern is laid over the surface, and with a stiff brush the pigment is removed from the parts which are to be transparent. The glass is next inclosed in a frame, and above it is extended a piece of tulle or, if desired, embroidered lace, the embroidery in the latter case being so disposed as to harmonize with the ground-pattern previously made. The whole is then hermetically closed in a box which contains in its lower portion a reservoir holding a certain quantity of dry color in the form of impalpable powder. This by an air-blast is blown evenly upon the glass and adheres to the latter wherever the surface is not protected by the threads of lace. In this way the pattern of the latter is defined. In order to fix the powder, the sheets of glass are placed in a steam-chamber where the steam moistens the gum and causes the powder to adhere. The color is then burned in a special furnace.

Variability of the Nebulæ.—In a lecture recently delivered at Paris, under the auspices of the Scientific Association of France, the eminent Swiss astronomer Wolf gave an account of recent researches on the "variability of the nebulæ." His conclusions, as stated in La Nature, are: that some of the nebulae are certainly in a state of relative motion—at least one double nebula being known to astronomers, the component parts of which revolve about each other; that in all probability some of the nebulæ are waning and disappearing—as instances of this he cites three nebulæ in the constellation of Taurus; that possibly some of the nebulæ are undergoing a change of form; the spiral nebula in Canes Venatici appears to afford an illustration of this fact. As for the distances of the nebulæ, they cannot yet be determined, but there are grounds for believing that many of them are not more remote from us than the fixed stars.

Copying Designs by Photography.—A new process of making photographic copies of machinery, drawings, plans, maps, etc., in blue lines on a white ground, has been invented by H. Pellet, a chemist of Paris. This process (says La Nature) is based on the peculiar property possessed by perchloride of iron, whereby it is converted into protochloride by exposure to light. The protochloride is not affected by contact with prussiate-of-potash solution, but the perchloride at once becomes blue. M. Pellet sensitizes a sheet of paper by dipping it in a bath consisting of water 100 parts, perchloride of iron 10 parts, oxalic or some other vegetal acid 5 parts. In case the paper was not sufficiently sized, gelatine, isinglass, dextrine, or some such substance, would have to be added to this solution. The paper so treated—M. Pellet calls it now cyanofer-paper—is dried in the dark, and may then be kept for a length of time. It is very sensitive to light. To make a copy of a drawing made on transparent paper, the drawing is spread over a dry sheet of the cyanofer, a plate of glass laid over all, and the whole exposed to the light. In summer, with exposure to the full sunlight, it takes from fifteen to thirty seconds to decompose so much of the perchloride of iron as is not protected by the lines of the drawing. In winter, an exposure of forty to seventy seconds is necessary. In the shade, in clear weather, the exposure varies from two to six minutes, and in cloudy or rainy weather, from fifteen to forty minutes. The electric light may be used instead of sunlight, the time of exposure varying according to the intensity of the light and the distance. After exposure, the paper is dipped in a bath of prussiate of potash (15 to 18 per 100 parts of water), and it at once