-1859] WRITINGS OF JOSEPH HENRY, 259 



with the water which passes through it into the ocean, if 

 transmitted by means of the telegraph, would be of the 

 greatest value, in connection with previous experience as to 

 the elevation of the water of the river corresponding to a 

 given indication of the rain-gauge, in furnishing the means 

 by which the effects of floods may be guarded against and 

 the labors of the husbandman along the banks preserved, 

 in many cases, from destruction. A single gauge in each 

 subordinate basin would be sufficient to furnish valuable 

 practical information of this kind, and in the case of the 

 Mississippi River, (especially if applied to the basins on the 

 eastern side,) would suffice to give premonitory indications of 

 a sudden rise at the lower part of the river, since the water 

 which is furnished from the western part of the valley of the 

 Mississippi is more constant in its amount, or in other words 

 not so subject to fitful variations. 



The simplest method of measuring the rain, which any 

 one may practice for himself, is to catch the water in a cylin- 

 drical vessel, like an ordinary tin pail, and to measure the 

 depth in inches and tenths of an inch after each shower. It 

 is hardly necessary to remark that the vessel should be so 

 placed that it may not be screened by trees, buildings, and 

 other obstacles from the wind which bears along the falling 

 drops. The object of the investigation is to ascertain the 

 number of inches of water which fall from the clouds on a 

 given space in a given time — for example, a year or a season. 

 It is well known that while the wind is blowing strongly 

 the drops descend in an oblique direction, and gauges have 

 been proposed which, by the action of the wind, would so 

 incline their mouths as always to present them at right 

 angles to the direction of the drops ; but gauges of this kind 

 would not give the indication required, which is that of the 

 absolute quantity of rain which falls on a given horizontal 

 extent of the surface of the earth. 



A remarkable fact has been observed as to the amount of 

 rain collected at different heights. It is a well known phe- 

 nomenon, of which we shall give the explanation hereafter, 

 that on the windward side of a mountain a greater amount 



