270 Mr. MeiJde's Reply to Mr. Holt [April, 



number for January he has favoured us with an article in which 

 he not only shows clearly that he has entirely misunderstood my 

 explanation, but that he, if possible, still labours under a 

 delusion superior to that of M. Flaugergues himself; who 

 probably fell into that unaccountable mistake merely through 

 haste, or from having his attention so much occupied with the 

 many interesting services which he renders to science. 



The Wernerian Natural History Society and the Bibliotheque 

 Universelle are both of high authority ; but an error is still an 

 error in these, as well as truth is truth, should it occur in a novel. 

 Unfortunately, however, for your correspondent, and the cause 

 he has so faithfully espoused, the position I advanced is inde- 

 pendent of authorities or opinions, since it must stand or fall 

 with some of the simplest truths of geometry. 



Indeed it is almost inconceivable how any one Avho is but 

 slightly acquainted with elementary geometry should feel the 

 least embarrassed on seeing clearly that the horizontal distance, 

 or distance of the points, in which the drops pass through a 

 plane parallel to the horizon, is absolutely independent of their 

 inchnation where the wind runs steadily and horizontally. This 

 I formerly showed, and shall now endeavour to do so again a 

 little differently. 



Let A C, B D, with the intermediate 

 parallels, represent the paths of rain- 

 drops falling perpendicularly ; and let 

 A E, B F, with the parallels between 

 them, be the paths of the same drops when 

 acted on by a steady wind blowing from 

 B to A. Suppose A B aiid E D paral- 

 lel to the horizon. Now since A C must be parallel to B D, and 

 A E to B F, we have EF = AB=CD. A gauge, therefore, 

 of the width C D would exactly receive the same quantity of 

 rain if placed at E F, let the inchnation be what it may. Con- 

 sequently the quantiti/ of water received hy a rain-gauge is totally 

 independent oft/ie general inclination of the rain. 



If F G be perpendicular to A E, it must no doubt be less than 

 E F. But however short F G may become, all the drops still 

 pass through it ; since the parallels A E, B F, &c. are only so 

 much the more crowded together. The grand principle, there- 

 fore, of M. Flaugergues'.s mistake is his always proceeding on the 

 supposition that the shortest or perpendicular distance of the 

 lines in which the rain falls is constant ; whereas that varies 

 with the sine of inclination ; while it is the distance of the points 

 in which the drops pass through a horizontal plane that is inva- 

 riable. Mr. Holt has duly adopted the same mistake, only try- 

 ing to improve upon it, by saying that the quantity of rain 

 received will be proportional to the angle of inclination ; whereas 

 M. Flaugergues makes it as the sine of tliat angle. 



As the rain drops, if first acted on by the wind, and afterward 



