184 ANNUAL OF SCIENTIFIC DISCOYERY. 



estinpf apparatus, othex' simple experiments can also be executed. 

 — Reader. 



.FALL, OF RAIN. 



The last wookly return of tlic Rt'Cfistrar-Gonoral j^ivos the fol- 

 lowiiij^ iuten.'sliiig iiirorniation in respect to rain-fall: "Rain fell 

 in London to tiio amount of 0.43 inch, whicJi is equivalent to 43 

 tons of rain per aero. An En^^lish acre consists of^G, 272,040 

 square inches ; and an inch deep of rain on an aero yields 6,272,040 

 cubic inclics of water, ■which, at 277,274 cnl)ic inches to the (j-allon, 

 makes 22,022.6 jx^dlons; and as a gallon of distilled water weighs 

 10 lbs., the rain-fall on an acre is 226,225 lbs. avoirdupois; con- 

 sequently an inch deep of rain weighs 100.09 tons, or nearly 101 

 tons per acre. For every KMlth of an inch, a ton of water falls ])or 

 acre." If any agriculturist were to try the experiment of dis- 

 tributing artiiicially that which nature so bountifully supplies, he 

 would soon feel inilined to " rest and be thanUI'ul." 



M. Petit, the director of the Observatory at Toulouse, speaking 

 of the late heavy rains, says: "The quantity is not so unusual as 

 at first sight would appear. The avci-age annual fall is about 60 

 centimetres, rather more than 2 feet English, spread over about 

 100 rainy d;iys, thus giving an average fall of al)out millimetres 

 for each day, or about litres, 10 to 11 pints English, per scjuare 

 metre. The average of the heavy rains of the 15th, 10th, and 

 17th of January, in the present year, rose to about 9 millinii'tros. 

 Greater falls have often occurred in Franco. On the lOth of 

 September, 1844, 35 millimetres of rain fell at Toulouse in 30 

 minutes ; and on the 10th of August, 1859, there fell 59 milli- 

 metres in two successive storms of about 40 miinites each in dura- 

 tion. In recalling the impression of terror created by the sight 

 of a precipice, one is inclined to ask how it is that we are not 

 teiTified at such enormous quantities of water being suspended 

 over our heads. But the question appears under a still more 

 extraordinary aspect, when we consider the amount of heat re- 

 quired to vaporize all the water which we receive in the form of 

 rain. When we remember that in the tropics there fall about 2 

 metres of water per annum, that in our climate we have never 

 less than 50 or CO centimetres, and that the masses of snow in 

 the polar regions must also furnish a great quantity of water, it 

 will be readily admitted that the annual rain-fall must be, at 

 least, equal to a stratum of water all over the gtobe of 50 centi- 

 metres, upwards of 19^ inches English. It is easy, with these 

 facts given, to see that the evai:)oration caused by the heat of the 

 sun must render to the atmosphere about 175,000,000,000 cubic 

 metres of water per day, or rather more than 2,000,000,000 of 

 liti'es a second. And yet the furnace is 38 millions of leagues 

 distant from us." — Journal oftheSoc. of Arts, Nos., Q39, 6'iO, 1865. 



