Open main menu

Page:Popular Science Monthly Volume 18.djvu/374

This page has been validated.

blasts, and that after three o'clock its motion was not interfered with, would indicate that more violent disturbances took place before than after that hour. A smaller anemometer of Robinson's model was torn from its fastenings between two and three o'clock, and so completely demolished that no record even of the work which it had already done could be obtained. This is much to be regretted, as otherwise a means of verifying the extraordinary velocity registered by the anemograph would have existed. Concerning the latter it should be said that, regarding the smaller anemometer as a standard, it has been found upon examination to somewhat over-estimate the velocity of very high winds, and to under-estimate those of low speed. At the same time it can not be positively stated which of the two instruments was in error.

A continuous record of the direction of the wind is kept. Upon examining this it is found that, during the whole of the period considered, the direction varied between north and west. Up to 1 a. m., of the 4th, the wind was steadily from the north-northwest. From that hour until 5 a. m., its fluctuations were confined between northwest and west. A decided change in direction seems to have taken place between the hours of two and three o'clock.

The early part of the storm was accompanied by an unusually heavy fall of rain. The violence of the wind prevented the reading of the rain-gauges during the night, but when emptied at 7 a. m. they showed a total of 4·66 inches, nearly all of which must have fallen during—at most—two or three hours.

It may be interesting to make some comparisons between the violence of this storm and that which was undoubtedly the immediate cause of the destruction of the Tay Bridge, on the evening of December 28, 1879. Unfortunately, it does not appear that any very exact or reliable observations of the velocity of the wind on that occasion were made; but an approximate measure of it may be obtained from the testimony of several of the witnesses, who were men of considerable experience in the observation and estimation of high winds. The following selections from the "Times" report of the Board of Trade inquiry are of interest in this connection. Captain Scott, R. N., who was superintendent of a training-ship stationed in the Tay, testifies that his barometer fell from 29·60 inches at noon to 29 inches at seven o'clock—that being the lowest point reached. Also, that, in the navy, storms were described by numbers from 1 to 12, 12 being the maximum. Upon that scale he would describe this storm in the Tay as from 10 to 11. He had on rare occasions in China and the West Indies rated storms as high as 12.

Admiral William Heriot Maitland Dougal, who had resided at the mouth of the Tay continuously for twenty-nine years, stated that his barometer fell from 29·40 inches to 28·80 inches. The difference between these and the previous barometric heights is easily explained by