Page:Proceedings of the Royal Society of London Vol 1.djvu/114

Rh observations which appear to him to conﬁrm what he had advanced on a former occasion touching the dispersive powers of the eye.

The ultimate results of the experiments made on this substance, which it seems had never before been properly analysed, are—that 25 grains contain 12% grains of argillaceous earth, 2 of silex, and 8 of iron; that 1 grain was not dissolved, and that the remainder, being 1% grain, was lost in the process. Another process gave the same components, but in somewhat diﬁ'erent proportions. These in- gredients being very similar to those found by Mr. Klaproth in Dia- mond spar, it is thought that emery is essentially a substance of the same nature, with perhaps a somewhat greater proportion of iron.

The remarks here brought forward relate chieﬂy to Dr- Herschel’s experiments on the solar and terrestrial rays that occasion heat, pub- lished in the Philosophical Transactions for the year 1800, and are meant to rectify some anomalies which appear in their results. The paper consists of two parts: the ﬁrst being the observations on Dr. Herschel's experiments, and some new ones, with inferences deduced from them; and the second the exposition of a theory, which the author thinks may reconcile all contradictions.

In the ﬁrst part he sets out with brieﬂy stating the manner in which Dr. Herschel conducted the experiments he made, in order to estimate, by the indications of different thermometers, the quantity of heat transmitted through various substances, compared with the heat aﬁcrded by direct rays from different luminous bodies, or more properly sources of heat. Here the author soon starts a difﬁculty concerning the mode of estimating the intercepting power of the substances used in the experiments. As these experiments consist of a series of observations made progressively at intervals of one mi- nute between each other, it follows that the ratio Dr. Herschel adopted between the heat produced by direct rays, and. those transmitted through coloured media, is not, as he imagined, a constant proportion, be having uniformly deduced his inferences from the differences between the initial and the ﬁnal degrees of heat; whereas, had he attended to the intermediate observations, he would have found that each of them would have afforded a different ratio.

Having maturer considered this subject, the author, adverting to this circumstance of the various proportions of heat progressively yielded in these experiments, observes, that it can hardly be conceived why the faculty of transmitting and intercepting heat should