METEOROLOGY. 397 



eter. Among those tried, the anemometers with the larger cups regis- 

 tered the most wind, or, in other words, required the lowest factors to 

 give a correct result. 



" 3. That with the large Kew pattern, which is the one adopted bj the 

 Meteorological Office, the register gives about 20. per cent, too much, 

 requiring a factor of about 2.5 instead of 3. Even 2.5 is a little too 

 high, as friction would be introduced by the centrifugal force beyond 

 what occurs in the normal use of the instrument. 



"4. That the factor is probably higher for moderate than for high 

 velocities ; but whether this- is solely due to friction the experiments 

 do not allow us to decide. - - - 



" The problem of the anemometer may be stated to be as follows: Let 

 the uniform wind with the velocity V act on a cup anemometer of given 

 pattern, causing the cups to revolve with a velocity v, referred to the 

 center of the cups, the motion of the cups being retarded by a force of 

 friction F ; it is required to determine v as a function of Y and F, F 

 having any value from 0, corresponding to the ideal case of a friction - 

 less anemometer, to some limit Fj, which is just sufficient to keep the 

 cups from turning. I will refer to my appendix to the former of Dr. 

 Eobinson's papers {Phil. Trans., 1878, page 818), for the reasons for con- 

 cluding that F is equal to V^, multiplied by a function of V-4-v. Let 

 V -^ V— c, F -^ v^=Vj tti6n if we regard ? and rj as rectangular co-ordi- 

 nates, we have to determine the form of the curve lying within the posi- 

 tive quadrant I 5;, which is defined by these co-ordinates. 



" We may regard the problem as included in the more general problem 

 of determining t; as a function of V and F where V is positive, but F 

 may be of any magnitude and sign, and therefore v also. Negative 

 values of F mean, of course, that the cups, instead of being retarded by 

 friction, are acted on by an impelling force, making them go faster than 

 in a frictionless anemometer, and values greater than Fj imply a force 

 sufficient to send them around with the concave sides foremost." {JSFa- 

 ture, July, 1881, xxiv, p. 253.) 



C. E. Burton describes as follows an integrating anemometer that gives 

 the quadrantal components of the movement of the wind: "A roller 

 with a spherical edge is made to revolve with a velocity proportional to 

 that of the wind as recorded on an anemogram. This roller presses on 

 a plane table carried by two mutually perpendicular pairs of rails in 

 planes parallel to that of the table. The lowest of the pair of rails is 

 supported by a frame carried on the extremity of a vertical shaft. The 

 point of contact of the roller with the table lies in the prolongation of the 

 axis of the shaft. The table can rotate with the shaft, but not inde- 

 pendently. By a simple arrangement the shaft and, consequently, the 

 table are caused to take up positions corresponding from moment to 

 moment with the direction of the wind-record on the anemogram. A 

 style concentric with the shaft presses lightly against a compound sheet 

 of tracing and carbonized paper attached to the under side of the table. 



