Page:Popular Science Monthly Volume 10.djvu/134

124 the entire sewage of Coventry in this way, including rent of land and interest on capital, and without deducting receipts from the sale of manure, is about 1s. 7d. per head of the population per year. But, taking into account the chemical value of the manure, the cost would be about twopence per head.

Construction of Water-Tanks.—A water-tank at the top of St. George's Hospital, in London, recently burst, inundating the wards and causing destruction of life and property. This tank, which held about thirty-four tons of water, was made of cast-iron plates half an inch thick, bolted together in the usual way; in form it was a square of ten feet on a side and the depth twelve feet. The thickness of the iron plates was adequate to resist the strain put upon them only on the usual condition of the employment of tie-bars and nuts of the needed strength. But, instead of adopting the proper plan of bolting these tie-bars directly to the flanges by which the plates themselves were bolted together, thin plates of wrought-iron, only one-quarter of an inch thick, were bolted to these flanges, and the tie-bars were attached to cross-pieces that ran through holes in these plates. The cross-pieces were so short that on the least disturbance one end might slip out of its place, leaving the entire stress on the other end and on the thin plates in which it rested. As was to be expected, the plates gradually rusted, and, when the corrosion had advanced so far as to allow the bolt to be torn away by that strain on the sides of the tank which the cross-bars were intended to resist, the tank tore in two, and the water made its escape.

Movements of "Cold Waves."—Prof. Loomis, of Yale College, contributes to the American Journal of Science and Arts, for July, the fifth of his valuable series of papers on "Meteorology."

In a former paper he presented facts showing the origin and probable cause of extremely low temperatures. It was found that they developed among the Rocky Mountains, and moved thence, as "cold waves," over the continent eastward. Since the publication of that paper this phenomenon has become well understood, and is now sustained by further proof. It appears that low temperatures follow in the wake of storms; or, in other words, areas of high barometer follow those of low barometer.

By low temperature is understood a degree of cold which is greatly below the mean temperature of the place or area where it prevails. Thus the cold wave of December, 1872, started in Dakota on the 16th, and the temperature fell to 15°, 25°, and finally 44°, below the mean of the month. At the same time the barometer rose to 30.64.

The cold wave moved eastward and southeastward, the barometer rising as the cold came on. The cold was extreme from the Rocky Mountains to Lake Michigan, and from latitude 38° to the British possessions.

In New York, during the last six days of the month, the depression of temperature ranged from 18° to 24° below the mean of the month.

It is quite obvious, Prof. Loomis observes, that the cold experienced in Dakota did not come from beyond the Rocky Mountains, but on the easterly side, near longitude 100°. The greatest observed cold in the instance referred to was not at the most northern stations, which strengthens the conclusion expressed in a former paper that there is a source of cold independent of the transfer of air from a higher to lower latitudes. As the cold wave moves eastward, the intensity of the cold is found to diminish.

The professor calls attention to the very interesting fact that, during the low temperature of December, 1872, the stratum of cold air was of no great thickness, probably not more than 9,000 feet, as was shown at Mount Washington. On the 26th of the month, when the cold was at its maximum over the region, it was found that the temperature was higher by 20° Fahr. at the summit of the mountain than at its base.

Further facts are presented in this paper, showing the general form of areas of low barometer and of high barometer. It was previously shown that a storm area is more or less oblong, and not in any observed case entirely circular. The same appears to be true of the cold areas.