Anemometers of Messrs. Whewell and Osier. 475 



had since received some valuable improvements, which were suggested 

 by the practical working of the machine. That he might not occupy 

 the time of the Section too long, it would suffice at present to say, 

 that in it a small set of wind-mill vanes, something like the ventilators 

 placed in our windows, were presented to the wind by a common 

 vane, let the direction of the wind blow how it might : the aerial 

 current as it passed set these vanes into rapid motion, and a train of 

 wheels and pinions reduced the motion, which was thence communi- 

 cated to a pencil traversing vertically, and pressing against an up- 

 right cylinder, which formed the support of the instrument, and that 

 10,000 revolutions of the fly only caused the pencil to descend the one 

 twentieth of an inch. The surface of the cylinder was japanned white, 

 and the pencil as the vane wavered kept tracing a thick irregular line, 

 like the shadings on the coast of a map : the middle of a line was 

 readily ascertained, and it gave the mean direction of the wind actually 

 exhibited before the eye by a diagram, while the length of the line 

 was proportional to the velocity of the wind, and the length of time 

 during which it blew in each direction j which therefore gave what 

 he called the integral effects of the wind, or the total amount of the 

 aerial current which had passed the place of observation in the di- 

 rection of each point of the compass during the interval which had 

 elapsed since the time of last recording the instrument. This, it was 

 well known, was a subject of much importance in meteorological 

 speculations, but has not been hitherto accomplished. It was in- 

 deed deemed of much consequence, to obtain even the mean direction 

 of the wind at a given place, and the celebrated Kamtz, in his Mete- 

 orologie, has made a collection of several results of this kind; but, in 

 the ordinary way of registering even the direction of the wind, which 

 is, by stating the length of time it blows from a certain point of the 

 compass, it is obvious that the velocity of the wind is altogether left 

 out of account, and therefore the high wind or storm of one day, is 

 placed on a par with the gentle breeze of the next, and therefore not 

 an attempt can be made to infer the total quantity, or what he had 

 ventured to term the integral effect of the wind. Mr. Whewell then 

 exhibited large diagrams, giving the results of the observations re- 

 corded at the Cambridge observatory, under the care of Professor 

 Challis, and at the house of the Cambridge Philosophical Society. 

 The similarity of the curves showed a general coincidence, but some 

 discrepancies were accounted for by the fact, that the dome of the 

 Equatorial instruments sheltered the anemometers placed at the ob- 

 servatory on the north side, while that placed upon the house of 

 the Philosophical Society was well situated for receiving the wind from 

 every quarter. Anemometers on this principle had been also erected 

 by Professor Forbes and Mr. Rankin, at Edinburgh, and by Mr. 

 Snow Harris and Mr. Southwood, at Plymouth ; but he was not at 

 present prepared to state the results of the observations made with 

 them, though he had little doubt they would be interesting and 

 useful. 



The President of the Section supposed it would rather suit the 

 convenience of the Section to hear Mr. Osier give the description of 



3 P 2 



