232 



The instrument consists of a fixed japanned cylinder, on which 

 the points of the compass are marked, and a moveable portion, 

 which revolves freely round the cylinder as the wind changes ; the 

 circular disk of a fly kept opposite to the wind by a weathercock 

 vane, is made to revolve with a velocity proportional to that of the 

 wind. The motion tlius produced is diminished by means of end- 

 less screws, working in a pair of toothed-wheels, and carried down 

 to a pencil, which, in its descent, rubs on the surface of the cylin- 

 der, and traces a broad line, whose length is proportional to the 

 velocity of the wind, and the time during which it blows from any 

 one direction taken jointly. The compartment of the cylinder on 

 which the marks are made indicates the direction of the wind. 



It was stated that the indications of this anemometer differed 

 from those of former ones, in so far as the integral effect of the 

 wind for any length of time, or the sum of all the elements of the 

 current, was recorded, and that the force of the wind was taken 

 into account along with the direction ; thus affording more satisfac- 

 tory data for meteorological speculations. This instrument was 

 erected on the roof of the University about the middle of Novem- 

 ber 18.37, and the register, as kept from that time till the 1st of 

 April 1838, was presented in a tabular form. 



The method of reducing these results was then explained. 

 Groups of neighbouring winds were taken, and all the intercardinal 

 were reduced to the cardinal points, by using certain multipliers, 

 found by considering each intermediate point as the hypothenuse of 

 a right-angled triangle; the east were subtracted from the west 

 winds, and the north from the south, and the two resulting effec- 

 tive winds compounded, gave the mean magnitude and direction for 

 the whole time during wliich the observations were made. These 

 results were given in Tables, and also in the graphical form. 



The observations with similar instruments at other stations have 

 not been published, and therefore no comparison of results could 

 be entered into. 



Monday, 1th January 1839. 

 Dr ABERCROMBIE in the Chair. 

 The following Donations were presented : 



Eulogy on Nathaniel Bowdich, LL.D., President of the American 

 Academy of Arts and Sciences. By John Pickering. 



I 



