On the Causes of the Tornado, or Water Spout. 161 
discussion sur ce point nous semblerait prématurée; il faut multiplier 
les observations, et constater avec plus de précision toutes les se 
stances de ces phénoménes.”* 
All the information respecting tornadoes afforded by Despretz is 
comprised in the following paragraphs, which I quote in his own words. 
““Trombe. La trombe se montre en mer et sur la terre; tantét 
elle semble sortir du sein de la mer, et s’éléve jusqu’aux nuages; tan= 
tot elle descend des nuages jusqu’a terre. 
“C’est une colonne d’eau cénique qui tourne sur elle-méme avec 
une grande vitesse; elle a quelquefois jusqu’a plus de deux cents 
métres de base. Elle est trés-commune entre les tropiques: les nay- 
igateurs passent rarement pres des cdtes de Guinée sans en aperce- 
voir plusieurs. 
‘Les trombes produisent des effets terribles ; elles déracinent les 
arbres, renversent les faibles habitations, soulévent les voitures, ete. 
**On peut se faire une idée des trombes par les tourbillons de pou- 
issiére qui se forment tout a-coup, en été, sur les routes, et qui tour- 
nent sur eux-mémes avec une grande rapidité.” 
In Nicholson’s Souci, quarto series, London, 1797, vol. 1, page 
583, there is an interesting account of some tornadoes seen from 
Nice; illustrated by engravings, by M. Michaud, who appears to con- 
sider them as the effect of electricity, and infers that he could produce 
the phenomenon in miniature by the aid of a machine, as thunder 
and lightning are by the same means illustrated. This I have found 
to be erroneous, as far as my experience goes, and from a cause 
which is, agreeably to my hypothesis, quite evident. I mean the 
absence of the co-operating influence of the air when emancipated by 
electric attraction from the confinement arising from its own weight. 
The theoretic remarks of Michaud are very brief, and, to me, 
scarcely intelligible, as he does not inform us in what way he suppo- 
ses the electric fluid to operate. 
T have understood, since I conceived my hypothesis, that Beccaria 
ascribed water spouts to electricity, but I have not had the advantage 
of learning by what reasoning he justified his inferences. However, 
should it appear that I have made, through the want of information, 
any undue claim to priority, I'shall cheerfully do justice to any phi- 
losopher whose speculations I may have overlooked. 
* Elemens de Physique Experimentale et de Meétéorologie, vo 727. 
bs sedis Wiarcdiaite de Physique, paragraph 656, p. 828, par i Despretz. 
21 
Vou. XXXII.—No. 1 
