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1812.
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Æt. 20-1.

full force—that is, immediately after you have first thought of them; for to delay until the subject in hand is exhausted would be to lose all the intervening ideas. Understand, too, that I preserve your communications as a repository into which I can dip for a subject requiring explanation, and therefore the more you insert the more will it deserve that name; nevertheless, I do not mean to desert one subject for another directly it is started, but reserve it as an after subject of consideration.

······ 'Sir H. Davy's book is, I understand, already published, but I have not yet seen it, nor do I know the price or size. It is entitled "Elements of Chemical Philosophy." ······ 'Definitions, dear A., are valuable things; I like them very much, and will be glad, when you meet with clever ones, if you will transcribe them. I am exceedingly well pleased with Dr. Thomson's definition of Chemistry; he calls it the science of insensible motions: "Chemistry is that science which treats of those events or changes in natural bodies which consist of insensible motions," in contradistinction to mechanics, which treats of sensible motions.

'How do you define idleness?

'I forgot to insert a query when at the proper place, though I think an investigation of it would be of importance to the science of chemistry, and perhaps electricity. Several of the metals, when rubbed, emit a peculiar smell, and more particularly tin. Now, smells are generally supposed to be caused by particles of the body that are given off. If so, then it introduces to