800 "Transactions.—Muüscellaneous, 
given by the anemometer at Sydney, during the recent great storm, when 
the amazing velocity of 153 miles per hour, equivalent to a pressure of 117 
pounds on the square foot was registered; being the highest ever yet 
recorded in any country; while several times during that storm a pressure 
of 112 pounds was indicated. i 
21. To appreciate the real meaning of such a tremendous pressure, the 
following illustration of its practical effect may be given :—A plate-glass 
window three feet square, a very common size, would receive a blow of 
1,053 pounds, or nearly half a ton. A sheet of plate-glass such as those 
of several shop windows in this city, viz., ten feet by five, would have to 
sustain a blow (not a steady pressure, be it remembered,) of nearly 6,000 
pounds, or almost three tons; while the side of a building 50 feet long and 
40 feet high—no extraordinary dimensions— would receive a lateral blow of 
284,000 pounds, or more than 100 tons. 
22. Buch would have been the dynamical power of the wind, if (1) its 
velocity were really that indicated by the anemometer on the occasion 
referred to; and (2) if that velocity actually represented the pressure 
deduced by the accepted formula. 
23. This latter point I do not purpose to investigate in the present 
paper, but I shall endeavour on a future occasion to show that there is good 
reason to doubt the correctness of the accepted ratio of wind-velocity to 
pressure. 
24. I now proceed to explain why I do not believe that the actual 
velocity of the wind, on the occasions of these extraordinary records being 
obtained, was that apparently indicated by the anemometer. 
25. In the first place, let it be clearly understood that the only point 
actually recordable by the anemometer is the number of revolutions made 
by its cups. From this datum simple multiplication gives the distance 
travelled by the cups. The accepted formula is, that a second multiplica- 
tion by 8 gives the distance travelled by the wind. Hence, in the Sydney 
storm, when the apparent velocity of the wind was 158 miles, the actual 
self-recorded speed of the cups was 51 miles, and the triple velocity was 
deduced on the adopted ratio of 3-1. But is this ratio applicable to all 
eonditions of the wind, to steady or unsteady breezes, to zephyrs or 
gales, to increasing or decreasing forces, or to sudden gusts or lulls? Ifa 
dead calm were followed by a gust, would the cups at once revolve at full 
speed in spite of their vis inertie? Or again, if a gale were suddenly suc- 
ceeded by a ealm, would the cups, at one instant revolving so rapidly, in the 
next moment become motionless? The reply is obvious: they would not. 
In the latter hypothetical case, the cups would continue to revolye by mo- 
mentum at least for several seconds. Proceeding further, suppose the cups 
