146 



BENJ. TIKE S, JR., DESCRIPTIVE CATALOGUE. 



pable of sustaining. The heights of the column in each leg 

 will be equal, provided that the legs are of equal bores ; but 

 unequal if their bores are unequal. For suppose the legs 

 equal, and the column of water sustained by the wind to be 

 three inches, the water in the leg which the wind blows into 

 will be depressed one and a half inch below 0, and raised 

 as much in the other leg. But if the bore of the leg which 

 the wind blows into be double that of the other, the water 

 will be depressed only one inch, whilst it is raised twice as 

 much, or two inches, in the other, and vice versa. 



For obtaining in this case the true height, Dr. Lind has 

 subjoined the requisite formulae. The use of the small tube 

 of communication, a b is, to check the undulation of the 

 water, so that the height of it may be read off from the 

 scale with ease and certainty ; and also to prevent the 

 water from being thrown up to a much greater or less alti- 

 tude than the true height of the column which the wind is 

 able at that time to sustain. The author has calculated a 

 table, by means of which, having the height of the column 

 of water sustained in the wind-gauge, the force of the wind 

 a foot square may be determined. 



When the height of the water is not exactly mentioned in 

 the table, then that height may be separated into such parts 

 as are mentioned in the table, and the sum of the forces an- 

 swering to such parts will be the force of the wind corre- 

 spondent to the height in question : thus, if the height of the 

 water be 4.6 inches, then this height is equal to 4+0.5+0.1, 

 which parts are all on the table ; therefore, 



