72 Scientific Intelligence. [Jan. 



lated into the Annals of Philosophy for August), that it was 

 not difficult to account for the difference in the quantities of 

 rain that fall into rain-gauges placed at different heights. 

 Your correspondent Mr. Meickle, in the Annals of Philosophy for 

 September, objects to the theory of Mr. Kerr and M. Flau- 

 gergues as unphilosophical ; and endeavours, by a mathematical 

 diagram, to show that, be the inclination of the rain what it may, 

 the same quantity of drops will be received by the rain-gauge. 

 It appears to me Mr. Meickle has taken a wrong view of the 

 subject, I shall endeavour to express my ideas in as few words 

 as possible. If the receiving surface of the rain-gauge be dis- 

 posed parallel to the horizon, it may be readily shown that 

 should the rain fall perpendicularly, it will receive its due propor- 

 tion ; but it may also be as readily shown that if the rain be 

 driven by a current so as to fall in an angle more or less inclined 

 to the horizon, the same quantity of rain can never enter the 

 gauge. Should the rain be blown in a direction parallel to the 

 liorizon, it is obvious none could enter : if the inclination be at 

 10°, the quantity received will be less than if the angle were 20°; 

 much less than at 30° ; and so on : so that the quantity received 

 will be always in proportion to the angle of inclination. The 

 annexed diagram will illustrate 

 the subject. Let a, h, c, d, 

 represent the vertical section of 

 the common rain-gauge ; « c or 

 b d perpendicular to the hori- 

 zon. If the rain be inchned at 

 45°, as Hit e a, f c, the quantity 

 which can enter through a h 

 will be as the rectangle con- 

 tained by e g, perpendicular to 

 e a or f c, and the side a h, 

 which rectangle is equal to about seven-tenths of the square of 

 ah. If the inclination equal 20°, as at h a, i k, the quantity 

 received will be as the rectangle under I m and ab; equal to 

 about one-third of the square of a b. If the inclination be 60°, 

 as at n a, o p, the receiving superficies will be equal to the 



17 



rectangle under n q and a i, about - of the square of a b. Thus 



it is evident that in no inclination can so great a quantity of rain 

 enter as when it falls perpendicularly. 



Perhaps the phenomenon of more rain being collected in a 

 low confined situation than in an exposed high one may be 

 explained thus : a current of wind, impinging the flat side abed 

 of the gauge, would be glanced round the edges a c and b d, 

 and also over the top a h, it would, therefore, sweep off a consi- 

 derable portion of the falling rain, and thereby induce a false 

 estimate ; the same cause operating in a much less degree in a 

 low or confined situation would necessarily occasion the ccaav- 



