Taiks of Comeis. 39D 
cavity, has not, so far as my knowledge extends, yet been 
accounted for. I would not have presumed to address you, 
had I been acquainted with even a plausible hypothetical ex- 
planation. Certainty cannot, perhaps, be attained; and | 
hope, if | accomplish nothing more, to direet the attention of 
yourself and learned correspondents to the subject,--so very 
peculiar, but yet | believe pretty well established by experi- 
ment. The water which flows from fountains we suppose to 
have been mingled with the atmosphere in a state of vapour, 
and to have fallen from thence in the form of rain; and that 
thus a perpetual circulation is kept up. This in many cases’ 
may be, and no doubtis, the true explanation of the origin of 
springs; but I apprehend that such springs should depend in 
a greater or less degree upon the quantity of rain which falls 
in that particular region where they are situated; and though 
it is true that, during periods of great drought, the dew is very 
abundant, I believe that very nearly all that is not consumed 
in the support of vegetation is re-evaporated by the sun, 
Would it be fanciful, sir, to suppose it possible that, as many 
springs receive their support from the exterior of the earth, 
others may be supplied trom the interior? It is pretty certain 
that our globe is intersected in various directions by caverns. 
The shock of an earthquake -will in a few moments pass over 
a continent; which is scarcely possible, were the earth an 
uninterrupted solid. May not such fissures be filled with 
water? I think it at least possible, perhaps probable, that 
water preserves a communication throughout our globe, at 
different distances from the surface, according to the forma- 
tion of the earth at any particular place. Now, if a passage 
be once opened for this subterraneous water, being specifically 
lighter than earth, the centrifugal force of our planet, revolv- 
ing on its axis, would raise it to the surface, and cause it to 
overflow ; and the supply being inexhaustible, and not affect- 
ed by the moisture or dryness of the weather, the fountain 
would be perennial. It is certain there are never-failing 
springs in situations where any explanation which I have 
seen cannot be entertained fora moment. If you think my 
communication worthy of notice, I should be pleased to see 
your thoughts on the subject in your very valuable Journal, 
Very respectfully, your humble servant, Le 
4. Tuils of Comets.—A correspondent inquires whether 
“the tails of Comets may be accounted for from the peculiar 
