The Eev. T. R. Eobinson's Description of an improved Anemometer. 171 



respects preferable to correct mechanically by applying to C an auxiliary force 



equivalent to the friction. Besides the saving of labour, it extends the action 



of the instrument ; as, from the data in the preceding note, it cannot move with 



less than 1-29 mile per hour. The dynamic effect of such a force, while the wind 



,.. ., 53 grs. X 5280 X 100 ,^^^„ ,r • 

 traverses 100 miles, = — ^ — - — =— -^ = 13321bs x 1 foot; it would, 



therefore, require a weight of 37 lbs. falling 36 feet. The locality does not 

 permit this; and I, therefore, purpose to use a remontoh-, wound up by a small 

 mill similar to the anemometer itself Perhaps an electro-magnetic machine 

 might be simpler ; the expenditure of zinc and acid would be trifling, and their 

 consumption proportionate to the work done. The chief difficulty would be the 

 inconstancy of the current. 



The vane V is three feet long by one and a half extreme breadth ; it also is 

 made of sheet zinc. From a wish to give it as little momentum as possible, it 

 was at first a light wooden frame covered with varnished calico, which the wind 

 soon destroyed. This axle turns also on balls. 



It remains to describe the self-registering apparatus; and first, that for the 

 space. 



My first intention was to adopt a form resembling the charts of wind- 

 paths given by Dr. AVhewell in his memoir, but in which the curves should 

 be drawn by the wind itself The arrangement I proposed was to make the 



«=F.0.64637{y(l.^.i2^)-l}; (4) 



which, with the above values of/ and {a - a') is 



u-v.o■,ml{^[^.l^y^}. (5) 



From this the following table is computed : 



F= 1"'M = l-'-asS F = 6" M = 0" -068 



2 0-469 7 0050 



3 0-240 8 0-039 



4 0-144 9 0031 



5 0-095 10 025 



It is evident that above 5" per hour the correction is insensible. 

 VOL. XXII. 2 A 



