The Rev. T. R. Robinson's Description of an improved Anemometer. 167 



was permitted to make a few revolutions to come to its speed ; and then the 

 counter was put in action for a certain number of revolutions of the arm AC, 

 generally 96. Tlie time was also taken to give the mean velocitj-. I found 



I did not venture higher velocities, as the apparatus was not strong enougn ; 

 but the above are sufficient to show that, after allowing for friction, the value 

 of m= 3-000.* 



• Some facts observed during these experiments may be deserving a record. 



1. The mouths of the hemispheres being covered -with paper, so that planes were substituted 

 for concaves, I found, with V= 12-80 feet, m = 5-041. 



2. Cutting away the central paper, so as to leave merely a ring 0'-2 broad, which (from what 

 has been observed with Pitot's tube) I thought might increase the effect, proved very disad- 

 vantageous. 



3. Making the cups segments of 220^ was also hurtful, for, with 



F= 13-87, )« = 5-220. 



4. A single hemisphere with a flat counterpoise presenting its edge to the air, gives 



F= 7-30, m = 3-700. 



5. With three arms, two carrying entire spheres, and one a hemisphere, 



V= 10-30, m = 7-900. 



6. Five vertical windmill-vanes (the best number), of the same outer diameter, but heavier, 

 and set at 45°, give, in 96 revolutions of the arm, 



F= 7-63. No. rev. = 4975. 



F= 12-29. No. rev. = 516-0. 

 The four hemispheres at the same time, 



F= 13-61. No. rev. = 141-2. 

 The tips of the vanes here move about 3-4 times as fast as the wind. 



