WIND. 9 



"RESISTANCE OFFERED TO THE WIND BY BODIES HAVING THE SAME CROSS-SECTION, 

 BUT OF VARIOUS SHAPES (FROM HUTTON'S 'EXPERIMENTS'). 



Proportional numbers. 



Cone, vertex towards the wind 126 



base to the wind 291 



Sphere 121 



Cylinder, end to wind 285 



Hemisphere, flat side 288 



round side 119 



The careful records which were kept at the Forth Bridge 

 works have done much to throw light upon this difficult subject. 

 The results obtained from the wind-gauges at these works 

 during a severe south-west gale, which occurred in November, 

 1888, are recorded in Chambers Journal of January 26, 1889, 

 from which I quote as follows : 



" The severity of the gales in November last (1888), as measured 

 by the recording instruments at the Forth Bridge, affords ample 

 evidence of the intensity of one of the most prolonged storms that 

 have been felt in Scotland for many years. The worst of these gales 

 was that which began early on the morning of the 16th of November, 

 and continued with but little intermission into the morning of the 

 17th. The wind blew from the south-west; and those in charge of 

 the Forth Bridge believed that, though blowing very hard on Friday, 

 the gale was, if anything, more severe in the early hours of the 

 following morning. 



" The Forth Bridge wind-gauges, situated on the old Castle of 

 Inchgarvie, are three in number. The large gauge presents an area 

 of three hundred square feet to the wind, and is fixed parallel to the 

 centre line of the Forth Bridge, being specially designed and erected 

 to test the pressure of wind over a larger area than that of the 

 gauges commonly in use. This gauge registered at 9 a.m. on the 

 17th of November, for the previous twenty-four hours, a maximum 

 pressure of twenty-seven pounds per square foofc. The small pivoted 

 gauge, which has an area of only one and a half square foot, and 

 which, by means of a vane, is always made to stand at right angles 

 to the direction of the wind, indicated a pressure on the same day of 

 thirty-five pounds per square foot ; whilst the gauge of similar 

 dimensions, but rigidly fixed with its face parallel to the centre line 

 of the bridge, registered on the same date forty- one pounds per 

 square foot, a pressure corresponding to a velocity of wind exceeding 

 ninety miles per hour. 



" It will be noted that the pressure per square foot on the large 

 gauge is considerably less than on the smaller gauges. This reading 



