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1830.] Such are the principal reasons which have induced me to believe in the existence of a limit to the tension of vapour. If I am correct, then there are at least two causes, each of which is sufficient to overcome and destroy vapour when reduced to a certain tension; and both of which are acting effectually with numerous substances upon the surface of the earth; and retaining them in a state of perfect fixity. I have given reasons for supposing that the two bodies named, which boil at about 600° F., are perfectly fixed within limits of low temperature which we can command; and I have no doubt, that nearly all the present recognized metals, the earths, carbon, and many of the metallic oxides, besides the greater number of their compounds, are perfectly fixed bodies at common temperatures. The smell emitted by various metals when rubbed may be objected to these conclusions, but the circumstances under which these odours are produced, are such as not to leave any serious objections on my mind to the opinions above advanced.

I refrain from extending these views, as might easily be done, to the atomic theory, being rather desirous that they should first obtain the sanction or correction of scientific men. I should have been glad to have quoted more experiments upon the subject, and especially relative to such bodies as acquire their fixed point at, or somewhat below common temperatures. Captain Franklin has kindly undertaken to make certain experiments for me in the cold regions to which he has gone, and probably when he returns from his arduous undertaking, he may have some contributions towards this subject.

Royal Institution, May 4, 1826.

On the Limits of Vaporization.

I was induced some time since to put together a few remarks and experiments on the existence of a limit to vaporization, which were favoured with a place in the Philosophical Transactions for the year 1826. When the experiments there mentioned were published, I arranged some others bearing upon the same subject, but which required great length of time for