Mr Forbes's description of a new Anemometer. 41 



I 4^ut. V=:20 



* 2 a mlog. 1.87312 



Vlog. 1,30103 



1. 2.23534! 



e = 3.733 log, 0.57209 



t zr 0«5 2am 



e + i= 4.233 log. 0.62665 ~W 



-^i-^ log. 0.05456' - . - - 2d log. 8.73687 



9.380 log. 0.97221 

 V^ =z 20 X 0.5= 10.000 



Deflection 0.620 feet. 

 We have already got the deflection when V — 40, 2.268 feet. 

 Put. V = 60 



2am log. 1.87312 

 Vlog. 1.77815 



e= 1.244 log. 0.09497 



/ = 05 2 am 



1. 2.23534 



e 4- t 1.744 log. 0.24155 M 



l±ilog. 0.14658 - - - 2d log. 9.16607 



25.200 log. 1.40141 

 V^ = 60 X 0.5 = 30.000 



Deflection 4.800 feet. 

 We have thus obtained Ft. DifT. 



V = 20 corresponding Defl. 0.620 



V = 40 . 2.268 1.648 



V = 60 4.800 2.532 



Of which the second differences are nearly constant. 



I have taken occasion to remark, that, although the spaces 

 be thus proportioned to the actual velocities, the number of 

 balls contained in each circular ring will not correspond to the 

 periods during which the wind has blown with the indicated 

 velocity; for the distri' uion of the spherules depending on 

 the revolutions of a sail, which will be proportional very near- 

 ly to the forces, or the squares of the velocities, the numbers in 

 each compartment will of course bear that relation, and, taking 

 the first degree of velocity as a standard, those in the second 

 must be divided by 4, in the third by 9, &c. 



It would, however, be quite practicable so to proportion the 

 distances of the rings, as to make the number of balls contain- 



