Whence, Sir, if you should think that these papers have truth, the great Diana of real philosophers, to patronize them, you will confer a favour upon me, by laying them before that learned Body. If, on the contrary, you should deem this confutation trifling or futil, I hope you will be humane enough to suppress them, and give me your objections; and by that means lay a still greater obligation on one, who has not the pleasure to be personally acquainted with you. From, SIR, Your very humble Servant, Erasmus Darwin, _Physician at Litchfield, Staffordshire_. March 23. 1757. +LETTER I.+ _To the very honourable and learned the_ PRESIDENT _and_ MEMBERS _of the_ Royal Society. [Read May 5, 1757.] Gentlemen, THERE is ever such a charm attendant upon novelty, that be it in philosophy, medicine, or religion, the gazing world are too often led to adore, what they ought only to admire: whilst this vehemence of enthusiasm has generally soon rendered that object contemptible, that would otherwise have long laid claim to a more sober esteem. This was once the fate of chemistry: the vain and pompous boasts of her adepts brought the whole art into disrespect; and I should be sorry, if her sister electricity should share the same misfortunes. It is hence the ingenious Mr. Eeles will excuse me, for endeavouring to lay before you my opinion on the ascent of vapours, tho’ it by no means coincides with that he is so strenuous to establish, and plucks a plume from his idol goddess electricity. The probability, supporting the hypothesis of Mr. Eeles, according to his own expressions, rests on this: “That every particle of vapour is endued with a portion of electric fire; and that there is no other sufficient cause assigned for their ascending.” (_Phil. Trans. vol._ xlix. _part._ i. _p._ 134.). My design is therefore first to attempt to shew, that another theory, founded on principles better known, will sufficiently explain the ascent of vapours: and then, that some kinds of vapours are not endued with a more or less than their natural share of electric æther. The immense rarefaction of explosive bodies by heat, depends either on the escape of air before condensed in them, or on the expansion of the constituent parts of those bodies. This distinction has not been sufficiently considered by any one to my knowlege; nor shall I at present amuse the Society upon this head; it being enough for my present purpose to observe, that they may be thus distinguished: where air is emitted, it cannot be condensed again into the same bulk by cold; but the expansion of heated parts of bodies, as soon as that heat is withdrawn, ceases to exist.