in Regard to Wind Pressures. 41 



Per sq. foot; 



Glasgow Observatory, 1879 ... ... ... 25 lbs. 



Glasgow Observatory, maximum, according to 



Trantwine ... ... ... ... ... 55 lbs. 



Liverpool Old Observatory, maximum, accord- 

 ing to Mr. Russell 71 lbs. 



Philippine Islands, instrument broke at ... 103 lbs. 



North America, locomotive blown over, pressure 



necessary ... ... ... ... ... 93 lbs. 



Great Britain, maximum, according to Rankine 55 lbs. 



Maximum in violent hurricane, according to 



Molesworth 49 lbs. 



Liverpool Observatory, 1868, sudden gust, 



according to Hartnup, Ostler's anemometer 80 lbs. 



During five years at Greenwich Observatory, 



maximum ... ... ... ... ... 41 lbs. 



In this list what strikes one most is the amazing dis- 

 crepancy which occurs between the records from New South 

 Wales and Victoria, and, unfortunately, it is with these 

 figures that we have mainly to do. It is quite incredible 

 (recollecting that 50 lbs. pressure means a violent hurricane) 

 that the wind should have attained in New South Wales a 

 force 80 lbs. per square foot greater than that ever experi- 

 enced in Victoria. . It must be concluded, then, that 

 anemometrical measurement is unsatisfactory; and most 

 persons will agree with the verdict of a competent judge 

 when he says " that anemometry, for engineering purposes, 

 is in a chaotic state." 



Even assuming, however, that storms have occurred 

 giving a pressure of over 100 lbs. per square foot, such 

 storms must be looked upon as highly phenomenal — of such 

 rare occurrence and so limited in area, that the chances of 

 any particular structure meeting such a gale are extremely 

 remote, and therefore all consideration of such pressures 

 may reasonably be neglected. 



The maximum assumed in Great Britain for engineering 

 purposes appears to range from 40 to 60 lbs., and most 

 important structures are designed to meet such a force. In 

 Victoria the Werribee viaduct is designed for a pressure of 

 50 lbs., and if we take a force varying according to the 

 considerations mentioned hereafter of from 50 to 70 lbs. per 

 square foot, we shall get as near a reasonable solution of the 

 first point in connection with the matter as we can expect 

 to attain. 



