216 Instructions for the Scientific ETpcdiiion 



angles to the vane, supported by two light bars running on friction- 

 rollers, and communicating with three spiral springs in such away that 

 the plate cannot be affected by the wind's pressure without instantly 

 acting on the springs, and communicating the quantum of its action 

 by a wire passing down the centre of the tube, to another pencil 

 below, which thus registere its degree of force. The rain is re- 

 gistered at tlie same time by its weight acting on a balance, which 

 moves in proportion to the quantity falling, and has also a pencil at- 

 tached to it, recording the results. The receiver is so arranged as 

 to discharge every half inch that falls, when the pencil again starts 

 at zero. 



It is probable that the results obtained with this instrument would 

 require correction for the varying effects of the eddy, which must 

 be formed behind the board before they can be considered as exact 

 measures of the pressure ; and the effects of variations of temperature 

 upon the force of the springs should be experimentally ascertained, 

 particularly in very cold climates. This latter point may be deter- 

 mined by measuring the compression directly by the application of 

 known weights. 



Another self-registering anemometer has recently been constructed 

 by Professor Whewell, which exhibits upon a diagram not only the 

 direction and force, but the direction and integral effect of the wind, 

 but which is more complex in its construction, and practically more 

 liable to derangement. 



In it a small set of windmill vanes, something like the ventilators 

 of windows, are presented to the wind by a common vane, in what- 

 ever direction it may blow. The current, as it passes, sets these 

 vanes in rapid motion, and a train of wheels and pinions reduces the 

 motion, which is thence communicated to a pencil traversing verti- 

 cally, and pressing against an upright cylinder, which forms the sup- 

 port of the instrument: 1000 revolutions of the fly only cause the 

 pencil to descend -^Q^h. of an inch. The surface of the cylinder is 

 covered with white paper, and the pencil, as the vane wavers, keeps 

 tracing a thick irregular line, like the shadings on the coast of a 

 map. The middle of the line may be easily traced, and it gives the 

 mean direction of the wind, while the length of the line is propor- 

 tional to the velocity of the wind and the length of time during 

 which it blovvs in each direction. 



Those who do not possess a register-anemometer may make use 

 of the common vane and Lind's wind-gauge. The position of the 

 former should be clear of all deflections and eddies from objects of 

 the same or a higher level, and of course its position with regard to 

 the true north should be clearly determined. In registering the di- 

 rection of the wind it may be sufficient to use only 16 points of the 

 compass. 



Lind's wind-gauge for measuring the force or momentum of the 

 wind is adjusted for use by filling it with water till the liquid in 

 both legs of the siphon corresponds with the 0° of the scale. It is 

 to be held perpendicularly, with the mouth of the kneed tube turned 

 towards the wind, and the amount of the depression in one leg, and 



