ON THE KEW OBSERVATORY. 129 



if the cylinders A and B were sunk into the neighbouring earth, and I hope 

 that we may at some future time be allowed a very little space for this 

 purpose *. 



The use of the plate rf' rf' and of the glass shade P, is to exclude rain from 

 B, and for protection. 



The platinum pivots and jewelled holes effectually prevent the inconveni- 

 ences of oxidation, &c., and the instrument performs its office with great 

 delicacy and fidelity- 



If it were required to be used occasionally as a rain-gauge ovAj, a funnel 

 might be fitted upon A ; if for a vapour-gauge only, the whole might be pro- 

 tected from rain by a sort of roof or covering placed at some feet above it. 



Vane. 



Our wind-vane, fig. 17, Plate XXXI., is rather more convenient and accurate 

 than a common weather-cock. A is a small brass tube at whose upper end is 

 fixed a hard steel cap with a conical cavity, which turns upon the hard steel 

 point of a little rod screwed into a brass cap B, and B is fixed upon a pole C ; 

 S N is a very light tin hoop, having the points of the compass painted upon 

 it, and attached by arms to A, therefore it is carried round by A ; D is an 

 index formed of a bent wire attached to B ; E is the vane fixed to A and 

 counterpoised by F. 



This instrument is so placed, that the point of D, and whatever letter 

 painted on S N stands above it, are always in the plane of the observer's eye 

 viewing it through the window B of fig. 2. 



Anemometers. 



Lind's anemometer, as usually made by Watkins and Hill, has been con- 

 sulted, but is so very much less sensible than is necessary, (for the liglitest 

 zephyr is as important, at least, as the stiffest breeze to electrical meteorology,) 

 that we Avere induced to try 



M. Guyofs, but with no better success ; I was therefore driven to the ne- 

 cessity of inventing a somewhat rude but far more efiicient expedient, which 

 we call our 



Balance anemometer. — This turns with a weight of ten grains (or less), and 

 can be made to carry as many pounds (or more). A (fig. 15) is a light feather- 

 edged deal board exactly 1 foot square ; B is a cross formed by two pieces 

 of wood and carrying A at 6'; a leaden counterpoise C, at V'; a little arm, 

 hook and scale-dish D, at h^; and a counterpoise thereto at bK B is sup- 

 ported by nicely-turned brass pivots running in two little pieces of glass tube 

 attached to the supports E E, which are firmly secured upon a large base F ; G 

 is a kind of sentry-box f, with a projecting roof for protecting D B, &c. from 

 the wind ; H is a little vane, and I a pin thrust through E E and the arm b-, 

 M'hen the instrument is not in use. The whole has a coat of hard white 

 paint. 



The application of this mechanism is obvious. When tiie flat front of A is 

 placed at right angles with the direction of the wind (Z), which can be done 

 with tolerable accuracy by the help of H, D rises with weights placed in the 

 dish proportional to the force of the wind acting upon the square foot A. 

 We measure by grains. 



Great improvements as to making it self-adjustable to the direction of the 



* It might then, perhaps, indicate more accurately a certain relation to the amount in 

 excess in evaporation, &c. from an aqueous surface on the earth. It should perhaps be 

 made to float upon such a surface in a little boat or buoy. 



t The inveiition of Sergeant Gallowav, who made nearly the whole instrument. 

 18M. ■ K 



