26 



this storm, and that which was undoubtedly the immediate cause of the destruc- 

 tion of the Tay Bridge, on tli3 evening of the 28th Deceniher, 1879. Unfortunately 

 it does not appear that any very exact or reliable obsersvations 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 liigh winds. The 

 following selections from the Times report of the Board of Trade impiiry, are of 

 interest in this connection. Captain Scott, E. N.— who was superintendent of a 

 training-ship stationed in the Tay, testifies that his barometer fell from 29. GO 

 inches at noon to 29.03 inches at 7 o'clock — that being the lowest point reached. 

 Also that in the Navy, storms were describsd by numbers from 1 to 12, 12 being 

 tlie maximum. Upon tlrat scale he would describe this storm in the Tay as 

 from 10 to 11. He had on rare ocjasions in China and the West Indies rated 

 storms as liigh as 12. 



Admiral William Heriot Maitland Dougal, w ho 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. Tlie difference between these and the pi-evious barome- 

 tric heights, is easily explained liy the fact that his liouse was at an altitude of 

 200 feet above the level of the sea. ' He declared that the gale^was like a typhoon 

 in violence, and that in all the time during which he had lived on the Tay, he 

 had never experienced a gale of eijual severity. In his opinion the velocity of 

 tlie wind was from seventy-five to seventy-eight miles [»er hour, ;uk1 that during 

 the lulls it would f;iU to something like thirty. 



Charles Clark, who was an amateur observer, gave evidence that 29.00 

 inches was the minimum point reached, and that lie had marked the storm 4 on 

 a scale of 6; and that he had never yet recorded 5 or G. 



Other witnesses testified in about the same way, all agreeing reasonabi}' 

 well as to barometric depression and probable velocity. 



On comparing these statements with those already made concerning the 

 recent typho ni here in Japan, it will be seen that both in barometric range and 

 in wind velocity, the recent storm considerably exceeded that which was the 

 occasion of the Tay Iirldge disaster. The barometric change wis not only greater, 

 but more sudden in the former than in the latter. Concerning the direct meas- 

 urement of the pressure of the windiu pounds perstjuare foot, it must be sai I that the 

 instruments for doing this are, at present, to a great extent crudj and unreliable. 

 It is generally assumed that the pressure is proportional to the square of the 

 velocity. Upon a S3,ile ahiptal by the SinitlHoniin Institution an;i by the 

 United States Signal Service, the velocity of twenty-five miles per hour corresponds 

 to a pressure of 3 lbs. per square foot. Assuming the correctness of this and 

 also of the law given above, the pressure per square foot in the Tay storm must 

 have been nearly 30 lbs. and in the recent typhoon here it must have been 

 nearly 50 lb,«. It was shown in the tests made upon the material of the Tay 

 Biidge, that it might have been expected to give way under a wind pressure 



