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those calculations has made the computed gravities in ge-neral too great: for though the ingredients in each mixturewere proportioned to one another by weight, the calcu-lations were inadvertently made as if they had been takenby volume. The discovery of this mistake I owe toMr. SchefFer, who gives a paper on this subject in theSjvedisti transactions for the year 1757.

The computed gravities being rectified, there appears toobtain, in several of the mixtures, some degree of whatthe above experiments strew not to obtain in those with anequal, quantity of gold; the compounds being of greatergravity, or more contracted in volume, than the two me-tals considered separately.

This excess of the experimental gravities above thecomputed is attributed by Mr. Schefter to the gravity ofthe platina being greater than that which I had assigned toit. Pie imagines, that particles of air, adhering in thecavities of the nigged grains, had occasioned them, whenweighed in water, to occupy a larger space than that oftheir own proper bulk; and that, when the platina wasmelted into a mass with other metals, it then discoveredits true gravity. On this foundation he endeavours to de-duce, from the specific weights of the mixtures, that ofthe platina itself; one of the most important points, as heobserves, in its philosophic history, that I had left undisco-vered. Though I failed, on account of the above inad-vertence, of. attaining to its true weight, my experiments,he thinks, lead to it; and from those experiments he con-cludes, that it is certainly more ponderous than pure gold.

This point seems to require some further examination:for such a conclusion is. not to be received without thestrongest proofs; and if the principle of induction is notperfectly just, it may give rife to fallacies of worse conse-quence than an error in the gravity of platina.

I have