S2 Mr Forbes's description of a new Anemometer. 



ed by a thermometer placed in the stream, is the most philo- 

 sophical. 



But the determination, however precise, of the velocity of 

 the wind at any moment, is of little importance to meteorology ; 

 and it is not till we can obtain some general register of the 

 state of the wind in the absence of the observer, by a machine 

 of sufficient simplicity to be generally adopted, that we can 

 hope to raise the philosophy of the wind to that importance 

 which I am disposed to think it deserves to hold in atmosphe- 

 ric science 5 and no period was ever farther from such an ac- 

 quisition than the present, when the anemometer is the most 

 neglected of all meteorological instruments. A register of the 

 force or velocity of the wind in the absence of the observer 

 must of course include the register of its direction. An in- 

 strument for the last purpose was contrived by one Michael 

 Lomonosow, as I found long after the contrivance I have now 

 to describe was formed ; but for the former and more important 

 object, no plan, as far as I know, has been proposed. 



The principle of my anemometer occurred to me several 

 years ago, and I sketched the idea of an instrument much in 

 its present form ; but having lately added some improvements, 

 and finding, after much occasional consideration, no funda- 

 mental defect, nor any notice of a similar contrivance, I have 

 been induced to draw up the following account, and submit 

 the principles to the test of theory. 



It is surprising that among the numerous modes of expos- 

 ing surfaces to the wind and computing its resistance, which 

 have been proposed during this and the last century, * no one 

 seems to have thought the deflection of bodies, exposing a given 

 surface to the current during the time of their fall by the ac- 

 tion of gravity through a given height, a suitable means of de- 

 ducing the deflecting force. I admit that the elevation of an 

 exposed surface constrained to move in the arc of a circle has 

 been employed for such a purpose, and the effect computed 

 by the sine of the elevation ; but the principal merit I claim 

 for the new anemometer is the absence of any constraint what- 

 ever, and the facilities it gives for direct computation, the 

 weight of the moving body being taken into consideration. 



• See the excellent Article Anemometer, in the Edinburgh Encyclo" 

 pcedia. 



