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THE POPULAR SCIENCE MONTHLY.

clearly visible except when viewed at the right angle. This property, however, has the great advantage that it makes retouching of the picture impossible. To remedy the inconvenience arising from it, M. Lippmann has devised an apparatus for viewing the pictures by the aid of which the proper conditions of the angle can always be obtained.

 

Toads and Cancers.—Toads were used during the last century as local applications for the cure of cancerous breasts. An account of a cure said to have been wrought by this means is given in Martin's Natural History, published in 1785, from a letter from a physician to the Bishop of Carlisle. The doctor had attended the operation for eighteen or twenty days, and was surprised at the result. The toad was put into a linen bag, all but the head, and that was held to the part. It was supposed to suck the poison till it swelled up and died. Then other toads were put on, and so, till the sore was cured. Sometimes they disgorged, recovered, and became lively again. Other authorities, the writer said, held that the toads did not suck the poison, although they admitted that the swelling and falling off dead was a general consequence of the application. Dr. Leonard G. Guthrie shows, in the Lancet, that a toad can not suck, but when injured or alarmed blows itself up to about twice its ordinary size, and when held and constrained for any length of time in a hot hand, sweats profusely and would probably soon die. The effect of the secretion when held on the hand is to cause dryness, numbness, and a tingling; which it probably did to the cancerous breast, giving a sort of relief to the pain.

 

A "Sanitary" Building.—Dr. W. Van der Heyden, of Yokohama, Japan, has designed a sanitary building, in which he seeks in winter to imprison the heat-rays of the sun, and in summer to admit the light while excluding the excess of heat; and at the same time to afford perfect ventilation and security against disease germs. The walls of the houses are made of air-tight boxes with sides formed of panes of glass, built upon one another, hermetically jointed with felt, and filled with a solution of alum; the roof is covered with cement. "A house built in such a way is an entirely closed hollow space, like a box itself, without windows or doors—no openings, and no fissures. It is practically impermeable to air, moisture, heat, cold, dust, microbes, and insects." At convenient intervals in the walls of rough plate glass are plates of polished glass, to be used as windows for looking out. "Doors are not wanted, because the entrance can be made through the floor by means of a lift or staircase from an underground room which receives no direct light from the sun. The walls of the underground room are made of ordinary bricks, plastered inside, and protected outside with a thick layer of clay to keep out moisture; it will be better to have these walls constructed with iron plates, as quick conduction of heat is the requisite here. The light for this room comes through glass boxes let in the four corners of its ceiling which forms the floor of the upper room. . . . There is a nice mild diffused light in the lower room which fully enables one to do any laboratory work, and is sufficient to read by." The walls are protected against freezing in winter by inclosing the whole building in a covering of window glass. In the summer the window-glass frames are put within the house, and furnish air cushions, still further preventing the accession of outside heat. Special arrangements are made for the renewal of air, heated in winter and sterilized at all times; and as the house is proof against the entrance of air from any other source, all microbes, disease germs, infections, and insects are efficiently kept out. The author has tried his house, and thinks well of it.

 

Temperature of the Interior of Trees.—The experiments of M. Prinz on the variations of temperature in the interior of trees seem to show that the sap contains large quantities of gas, which escapes with a sound often quite marked, and which can sometimes be heard two steps away. The mean annual temperature of the interior of a tree corresponds with that of the external air; but the monthly mean sometimes varies by two or three degrees. It usually requires about a day for a fluctuation of temperature to be transmitted to the heart of a tree. While the difference between the interior temperature of a tree and that of the air is