Dr Fleming on a Simple Form of Rain- Gauge. 183 



the rain-drop, it likewise, in its turn, is modified in its hori- 

 zontal direction by every projecting obstacle, and deflected, 

 according to circumstances, laterally, upwards, or down- 

 wards, carrying the rain-drop along with it in its course. 

 Whoever has watched the falling of i*ain under the influence 

 of wind, and in the neighbourhood of houses, walls, or other 

 obstacles, must have observed, as the result of the eddies 

 generated, that it is deposited in defect in some places, and 

 in excess in others. In the case of falling snow, the derange- 

 ment is of the same character, but more obvious. Had these 

 influences been duly attended to, there would have been fewer 

 confident assertions respecting the smaller quantity of rain 

 which falls on elevated buildings than at lower levels, and 

 more inquiry respecting the cause of a less quantity being 

 collected in such circumstances. 



When a rain-gauge is elevated three or four feet above the 

 level of the ground, it is easily observed and emptied of its 

 contents, and, in calm weather, may be considered trust- 

 worthy. During a moderately stiff breeze, however, the rain- 

 drops may be seen whii'led about in the funnel, and even 

 carried out and lost after they had nearly reached their des- 

 tination. But independent of the eddies in the funnel, there 

 are deflections of the current produced externally, which ex- 

 ercise corresponding influence. 



The late Mr Thorn of Ascog, Bute, a well-known and ju- 

 dicious hydraulic engineer, was in the habit of measuring 

 the fall of rain, in order to predicate respecting the quantity 

 of water which might be derived from a natural or artificial 

 lake or pond, as a motive power for mill purposes. The gauge 

 which he employed was similar to the one figured by Cavallo, 

 in his " Natural Philosophy," vol. ii., p. 424, tab. xv., p. 3. 

 It was defective, however, in the want of a rim to the funnel, 

 so as to prevent the dispersion of any drops impinging di- 

 rectly on the sloping sides. But if defective in respect of the 

 rim, the position which he assigned to the gauge itself, namely, 

 placing it in a grass plot, and on a level with the surface, 

 constituted a decided improvement. The mouth of the funnel, 

 although unnecessarily large, does not present space enough 

 to permit any perceptible acceleration of the current of wind, 



