282 " Protection against Hail Storms. 



The tin point at top should be one and a half inch thick and 

 eight inches long, placed in direct contact with the tow yarn. 

 The hail rods should be about six hundred feet apart, and fixed 

 upon the most elevated points, such as the tops of hills, roofs of 

 houses, or trunks of stout trees. The cost is about a franc a 

 piece, (twenty cents,) and they last at least fifteen years." 



These hail rods, so simple in their construction, and easily ob- 

 tained in every part of the country, have now, we believe, been 

 in use nearly twenty years in France and Switzerland. Many 

 extensive districts in both these countries, which formerly suf- 

 fered severely from hail storms, and in which the crops and vine- 

 yards were subject almost annually to great destruction, are, 

 since the paragrele has been generally adopted, protected almost 

 entirely against their desolating effects. The Linnaean Society 

 of Paris, some time since, with a commendable zeal, made ex- 

 tensive inquiries in all parts of the Continent respecting the util- 

 ity of this instrument, and the result, as exhibited by them, 

 proves the paragrele, in all districts hable to hail storms, to be an 

 invention truly invaluable. Pubhc experiments were made in 

 such parts of the country as were most subject to hail showers, 

 and while those districts where paragreles had been erected were 

 quite protected, neighboring districts not guarded by these hail- 

 rods, were, as before, much devastated. The Society, drawing 

 their conclusions from the facts elicited by the various trials 

 made in France, estimated that the annual saving which would 

 arise from a general adoption of the paragrele, Ihroughout that 

 country, would not be less than five milhons of dollars . 



Considerable difference of opinion exists as to the method by 

 which the paragrele produces its effects. A commonly received 

 theory, based on the supposhion that hail is produced by a con- 

 gelation of the drops of water, in very elevated strata of the 

 atmosphere, is, that the hail rod, by attracting and detaining these 

 vapors in a lower stratum than that in which freezing takes place, 

 prevents its formation. But as hail storms are generally accom- 

 panied by thunder and lightning, an American writer has suggest- 

 ed that the paragrele acts by abstracting the superabundance of 

 electricity from highly charged clouds. The formation of hail, 

 according to this writer, takes place only when, by the sudden 

 passage of the electric fluid through the cloud, a portion of the 

 water is decomposed, and returns into its original gaseous state, 

 the heat abstracted (by the change from a liquid to an aeriform 

 state,) from the neighboring particles (or clouds ?) is so great as 

 to convert them into ice, when they descend in the form of hail. 

 The decomposition of a single cubic inch of water, according to 

 the tables of Biot, will reduce the temperature of 5.64 pounds 

 of water from 72° to 32°, the freezing point of Faln-enheit. 

 The decomposition of water by the electric spark is now a well 



