444 



The Rev. H.Lloyd on the Meteorology of Ireland. 



la order to know the amount of confidence which may be placed iu such 

 observations, it is necessary to determine how far, in respect of accuracy, six 

 degrees of wind-force can be estimated, the observations being supposed to 

 be made by practised observers. And to be able to apply the observations, we 

 must further know, what are the pressures and velocities of the wind corres- 

 ponding to the several terms of the scale. For these purposes I made a somewhat 

 extended series of observations, estimating the force of the wind according to 

 the prescribed scale, and, at the same time, measuring its velocity by means of 

 Robinson's anemometer. The following Table gives the mean results of these 

 observations. The numbers in the first column are the terms of the scale ; those 

 in the second are the corresponding times of 100 revolutions of the instrument, 

 expi-essed in seconds ;* the third column contains the corresponding velocities 

 of the wind, in feet per second ; and the fourth the calculated velocities, de- 

 duced as hereafter described. 



Table XXI. Velocities of the Wind corresponding to the Terms of the 



Scale (0 - 6). 



* Dr.lioBlNSON has shown (Transactions, vol.x.xii. p. 167), that the velocity of the wind is to that 

 of the centres of the hemispherical cups, as 3 to 1 . But r being the length of the horizontal arms of 

 the instrument, measured to these centres, the circumference of the circle described by them is 2'rr ; 

 and if r be expressed in feet, and n be the number of revolutions performed in a second, their 

 velocity is 2Trr ■< n. The corresponding velocity of the wind therefore is V=6^r.< n. In the 



instrument in my possession, the radius is 5-5 inches. Hence 2r = — , and substituting for tt 

 its numerical value, V = 8'64 x n. 



Instead of noting the number of revolutions, and parts of a revolution, performed in a given 

 time, I have found it convenient to observe the time of performing 100 revolutions. I have had 



