Page:Popular Science Monthly Volume 18.djvu/372

358 during the most interesting period; i. e., from 8, on the 3d of October, to 2 , of the 4th. Previous to one o'clock on the morning of the 4th but three observations are recorded: at 7, at 2 , and at 10 These indicate a steady decline in the barometer, and it is not likely that any extraordinary fluctuations occurred during this time. After 1, the observations were made hourly, and during a considerable portion of the time they were half-hourly. It will be seen, however, that a very important portion of the curve, from 10 to 1, is doubtful, and it is not at all unlikely that, had intermediate observations been recorded, the fall of the barometer would have appeared much more sudden than it does. The minimum observed height was 28·735 inches at 2 At three o'clock the height was only a trifle greater than this, and, from the nature of the curve before and after the interval from two to three o'clock as well as from the velocity of the wind, it seems highly probable that between these hours a lower point than any observed was reached. The curve is constructed to show the actual vertical movement of the mercurial column. From the minimum it rose rapidly until 6, at which hour the height was 29·386 inches, and from that hour the rise continued with less rapidity but with great steadiness, until the night of the following Wednesday, when the reading was 30·378 inches. Thus the range of the barometer in three days was 1·643 inches. This is more than two tenths of an inch greater than the range for the whole of the last year. At no time during last year did the barometer reach so low a point as 29 inches, and the mean height for the year was 29·952 inches.

The second chart shows the velocity of the wind at different hours, extending over the same interval of time. These velocities are computed from a continuous record made by an anemograph consisting of a Robinson's anemometer with Beckley's registering apparatus attached. From this curve it will be seen that, so far as the wind is concerned, up to about 11, there were no indications of the coming storm. At that time a breeze sprang up, which continued at less than twenty miles per hour until about 1 when it suddenly increased in velocity, and at 2  the record shows a speed of sixty miles per hour. Unfortunately, shortly after two o'clock, the clock-work which keeps the registering portion of the apparatus in motion was stopped, the motion of the pendulum being undoubtedly arrested by a sudden blast of great violence. This stoppage was not discovered until 3, so that between these hours the record is lost. At three o'clock the instrument was put in motion again, and, for about fifteen or twenty minutes after that hour, the record shows the extraordinary velocity of ninety-five miles per hour. From this time the violence diminished rapidly, a velocity of fifty miles per hour being registered at 4, and at 5 it had fallen to less than twenty miles per hour. Twice afterward, as will be seen by the chart, the speed