SCIENCE 



NEW YOEK, SEPTEMBER 22. 1893. 



THE AUGUST STORMS.* 



BY WALTER C. KERR, NEW BRIGHTON, STATEN ISLAND. 



The liavoc wrought upon vegetation in the vicinity of 

 New York city by the recent storms perhaps deserves no- 

 tice, especially considering the opportunity afforded to 

 compare the effects of two destructive gales, only four 

 days apart. These storms though quite similar in general 

 character differed widely in one feature, whose destruc- 

 tive power might escape general notice or at least be much 

 underrated. This feature is the amount of water in the 

 air, which largely augments the weight of the moving col- 

 umn and at high velocities transforms the usually harm- 

 less wind into a formidable battering ram. 



Some time since Mr. William T. Davis, of New Brighton, 

 Staten Island, mentioned that the comparative scarcity of 

 large trees in that vicinity was probably due to high gales, 

 and when the results of recent storms are viewed, there 

 can be little doubt regarding this cause. 



The gale of August 24 is generally credited with hav- 

 ing uprooted or broken more trees in this locality than 

 any on record. This destruction of vegetation was wide- 

 spread. In the cities and towns the streets were blocked 

 with fallen trees and branches while the country roads 

 were in many places impassable. Numerous white oak 

 and chestnut trees were ujjrooted that to all appearances 

 should have offered great resistance. This storm had a 

 comparatively low wind-velocity, and a great rainfall. 



The gale of August 29th caused some damage to vegeta- 

 tion, though not nearly so much as that of the 24th. At 

 sea it was one of the worst storms experienced in this lati- 

 tude for years. It was characterized by a very high wind 

 with little rain. 



It may be said that the first storm destroyed the weak 

 trees, leaving little for the second and greater one to 

 wreck. On the other hand it may be presumed that the 

 first storm would cause much weakening and facilitate the 

 efforts of the greater wind that followed. 



The first storm had a maximum velocity of forty-eight 

 miles, reached by our winds about once each month with- 

 out sensible damage, while the maximum velocity of the 

 second, sixty miles, is attained less frequently than once a 

 year and only rarely is this high rate destructive to veg- 

 etation. 



The following official records from the United States 

 Weather Bureau, N. Y., furnish accurate comparisons : 



August 2i, rainfall 3.81 inches from 7.52 P. M. August 

 23d to 8.15 A. M. August 24. 



Time, 12 12345678 



Wind velocity, 29 33 27 28 29 30 23 20 



Maximum velocity for one hour, thirty-seven miles at 2 

 A. M. 



ccent meeting of the Natural Science* Association of 



Maximum rate for one mile, forty-eight miles between 1 

 and 2 A. M. 



Between 2 and 3 P. M. August 24, the wind averaged 

 thirty-five mUes, with a maximum rate for one hour of forty- 

 two miles. At this time no rain fell and no damage re- 

 sulted. 



August 29, rainfall .28 inches from 4 A. M. to 8 A. M. 

 Time, 12 12345678 



Wind velocity, 24 31 33 38 38 44 40 32 



Maximum velocity for five minutes, fifty-four miles at 5 

 A. M. 



Maximum rate for one mile, sixty miles at 5 A. M. 



At this station of the United States Weather Bureau a 

 wind velocity of forty to fifty miles is attained once a month, 

 a wind velocity of sixty miles is attained scarcely once a 

 year, a wind velocity of seventy- two miles is the highest 

 on record. 



These figures show conclusively that, as ordinarily 

 measured, the second storm was by far the greater; in 

 fact, as the wind pressure is proportional to the square of 

 the velocity, it may be seen that the effect due to wind pres- 

 sure alone on August 29, should have been nearly double 

 that of August 24. 



When we, however, give value to the relative rainfalls, 

 3.81 inches as against .28 inches, the destructiveness of 

 the wet gale of August 24 becomes apparent. 



In a storm a tree must resist a column of air moving at 

 a high velocity and to a large degree consume its energy. 

 This energy is proportional to the mass and the square of 

 the velocity. Dry air has small mass per cubic foot, yet 

 at forty miles per hour yields a pressure of eight pounds per 

 square foot; at fifty miles twelve pounds; at sixty miles 

 eighteen pounds; at eighty miles thirty-two pounds; and 

 at 100 miles fifty pounds. If we add to each cubic foot of 

 air one-tenth of one per cent, by volume, of moisture, as, 

 for instance, by partly filling it with rain drops, its weight 

 will be nearly doubled(.0753 plus .0625), and in consequence 

 the energy of the moving mass will be Likewise doubled. 

 One-half of one per cent of water added to the air increases 

 the energy five-fold, and thus the wind at its maximum 

 velocity of forty-eight mHes on August 24, if burdened 

 with this amount of moisture, would have an effect greater 

 than a dry hurricane of 100 miles. When rain falls in calm 

 but little water is contained per cubic foot of air, but with 

 high winds the rainfall of a large area may be carried 

 along nearly horizontally and massed where intercepted 

 by vertical obstacles. It is therefore reasonable to pre- 

 sume that trees in exposed situations receive vastly more 

 water per square foot of surface than is measured by rain 

 gauges in the usual way. 



When wet the resistance of foliage to jjassing wind and 

 rain is doubtless increased, especially when there is a ten- 

 dency for the leaves and branches to mat together on the 

 windward side, while the weight of water carried by the 

 tree may be a considerable additional burden. 



It thus becomes easy to appreciate the enormous part 

 which water plays in the destructive force of high winds 

 on exi^osed trees, as well as on the more commonly noticed 

 windfallen grain and corn. 



