Lastly, the same law is traced in the constitution of the chlorides of the magnesian class of metals, which are found to have two equivalents of water strongly attached to them, and which may therefore be considered as constitutional. Many of them have two or four equivalents more, the proportion advancing by multiples of two equivalents.
Professor Graham has supported these views, not only by numerous arguments, but also by experimental investigations of the physical properties of different classes of salts, and a great number of chemical analyses; and he has thus largely added to our positive knowledge of this somewhat neglected branch of chemical science.
The Council, without pronouncing any judgement on the question whether Professor Graham's hypothesis concerning the different functions of water in the constitution of salts be a representation of the real mechanism of nature, are of opinion, that the discussion of his new and ingenious views will be highly conducive to the progress of science, particularly in the department of organic chemistry, in which they have been already followed out with success by some eminent foreign chemists, and have accordingly awarded to Professor Graham the Royal Medal for Chemistry of the present year, for his valuable researches in this department of science.
The Council have awarded the Rumford Medal to Professor Forbes, for his discoveries and investigations of the Polarization and Double Refraction of Heat, published in the recent volumes of the Transactions of the Royal Society of Edinburgh.
That solar heat, like the light which it accompanies, may be polarized, was shown by the early experiments of MM. Malus and Berard; but the announcement of M. Berard, that heat from other sources was also capable of polarization, not having been confirmed in subsequent repetitions of his experiments by other philosophers, it became of the highest importance to establish this analogy between light and heat from whatever source the latter might be derived.
The admirable instrument, the Thermo-multiplier, invented by MM. Nobili and Melloni, afforded facilities for the prosecution of inquiries of this nature, of which the inventors and others were not tardy in availing themselves. One of the most important results obtained by M. Melloni, and confirmed by Professor Forbes, the refrangibility of non-luminous heat by a prism of rock-salt, appeared to point to the polarization and double refraction of heat as almost necessary consequences. The experiments, however, of both these philosophers with tourmaline, undertaken nearly at the same time, appeared to negative the fact; but Professor Forbes becoming sensible of the source of error, in the conclusions he had at first drawn from his experiments, soon saw that his results clearly indicated the effect he was in search of. His subsequent experiments established the fact, that in the transmission of heat from an Argand lamp, from incandescent platinum, and even from non-luminous heated brass, through slices of tourmaline cut parallel to the axis of the crystal,
