io HARBOUR CONSTRUCTION. 



corresponds "with all previous experience at the Forth Bridge, and 

 would seem to indicate that the pressure on the small gauges must 

 be due to ' threads of air ' of limited area and high velocity, which, 

 when integrated over a large surface, produce an average pressure of 

 considerably reduced intensity." 



The foregoing agrees closely with information which the 

 resident engineer at the Forth Bridge works (Mr. F. E. Cooper, 

 M. Inst. C.E.) kindly furnished to me. 



Notwithstanding the foregoing generally admitted facts, it 

 may be useful to give the pressures which are commonly asso- 

 ciated with wind velocities, as it is likely these will continue 

 to be adopted until some better method of computing them than 

 at present exists has been discovered. 



For convenience of reference, I have therefore incorporated 

 these in Fig. 5. 



The pressures represented by the full curved line are those 

 usually associated with the relative wind velocities. In view of 

 the uncertainty which surrounds this subject, they must, however, 

 only be taken as approximately correct. 



The most recent investigations tend to show that the usually 

 accepted wind pressures at all events, when applied to large 

 areas are too high, and that those indicated by the dotted 

 curve are probably the more accurate. 



The following particulars, relative to the great storm of 

 November 17 and 18, 1893, were issued from the Meteorological 

 Station at Deerness, Orkney : 



" A hurricane of unprecedented violence passed over the north 

 of Scotland on the evening of the 17th and morning of the 18th. 

 The hurricane commenced exactly at 6 p.m. like the shot of a gun, 

 and during the first hour reached a velocity of 77 miles the previous 

 hour being only 14 : and attained its maximum velocity from nine 

 to ten at the rate of 95 miles, seven miles stronger than any one 

 previously recorded from Orkney. The weather for the week pre- 

 vious was extremely fine for November, although some indication of 

 the fearful hurricane was given by the gradual falling of the 

 barometer, which on the llth, at 9 p.m., had reached the unusually 

 high figure of 3O563 corrected, and gradually fell till 1 p.m. on the 17th, 

 when it reached the minimum of 28*599. After that, owing to the 

 approaching north wind, it gradually rose again. The barometric 

 readings corrected are llth, 9 p.m., 30' 563 ; 16th, 9 p.m., 29*368; 

 17th, 9 a.m., 28747; 17th, 9 p.m., 28757; 17th, 1 p.m., 28*599. 



