Page:Popular Science Monthly Volume 26.djvu/878

858 than red. Mixtures of linseed-oil and gypsum were eaten freely, but not so freely as the whiting mixture. Carbonate of baryta proved to be poisonous to the animals, but the poison seemed to be neutralized when carbonate of lime was mixed with it. Carbonate of lead seemed to act as a poison, but not so deadly, provided it was mixed with whiting, as it might have been supposed to be. Clay was not appreciated by the mice, but was eaten when mixed with whiting. Experiments with various results were also tried with sulphate of baryta, silica, carbonate and oxide of zinc (both eventually producing death), slaked lime (of which only one of the mice would eat enough to kill him), and whiting and sirup, which was eaten freely. Similar experiments were tried on rats, with similar results.

Rainfall as affected by Wind.—The proper construction and location of rain gauges to secure measurements agreeing with the average rainfall on the surrounding district has been a much-discussed problem. In 1766 Dr. Heberden observed that gauges on the ground collect generally a larger quantity of rain than gauges on the sides and roofs of buildings. As a summary of facts since learned, G. E. Curtis, in "Signal-Service Notes," No. 16, quotes the following from an article published by Symons in 1878: "The greater part of the decrease is due to wind. The stronger the wind, the greater the decrease with elevation. The less the diameter of the elevated gauge, the less will it indicate. A gauge on the leeward side of a tower may collect as much rain as one on the ground. A gauge in the middle of a large roof may, notwithstanding its height, collect very nearly the same as one upon the ground." In the following year Symons further stated that "there is no evidence of any difference between the fall of rain at various-heights from sixty to two hundred and sixty feet above the ground." How the variation in the vicinity of buildings can depend on the wind was explained in 1861 by W. S. Jevons, who said that a stream of air meeting an obstacle leaps over it, flowing with increased velocity above it, as a river flows fastest through narrows. When two equal drops of rain fall into a current of air at points where the velocity is not the same, one drop will either approach toward or recede from the other, and the quantity of rain falling on the space beneath will be increased or diminished. The large rainfall registered at the Signal-Service station on Mount Washington has recently been specially investigated. Four extra gauges, three inches in diameter, were set up seventy-five feet respectively north, east, south, and west from the station-gauge. The observations of thirteen months showed that precipitation varies materially within one or two hundred feet. It was found also that the windward gauges generally recorded the least rain, the central gauges more, and the leeward gauges the most. Hence it is concluded that the wind affects the distribution of rain on the summit of Mount Washington in the same way as on the tops of buildings. During this period the station gauge, which is eight inches in diameter, was found to give larger readings than the others, and a three-inch gauge was set up near the large one for comparison under the same conditions. The conclusion reached was that the discrepancy was due to insufficient collection by the smaller gauge, and varied as the square of the wind's velocity. European observers have noticed no such differences between the measurements of three-inch gauges and larger sizes, but their observations were made when the velocity of the wind did not exceed twenty miles an hour, while on Mount Washington it reached seventy-five miles an hour.

The Food of Animals.—The question whether the distinction between herbivorous and carnivorous animals is as clear as it has been supposed to be is discussed in the "Field Naturalist" and the "Journal of Science." The prevailing theory is that the primary animal life was herbivorous; and this must have been the case with the earliest and lowest forms, which had nothing but plants on which to feed; but among vertebrates, and especially among mammalia, the earliest forms seem to have been zoöphagous or animal-eating. Among fishes, amphibians, and reptiles, even in the earlier geological epochs, the vegetable feeders are found in a minority. The earliest fossil