but both of them place a limit to the solar life. In the case of the meteoric theory, it cannot be supposed that the supply of meteors is inexhaustible; we must look forward to the time when every stone wandering in the planetary spaces shall have fallen into the sun, and when, therefore, the supply of heat shall cease, a time to be followed at no great distance by the dying away of the solar light. Since a mass of matter cannot go on contracting for ever, it is evident that the shrinkage theory, like the meteoric, cannot invest the sun with the attribute of permanence. In this respect they both fail to commend themselves to the mind, as has been said by Sir W. Siemens : "If either of these hypotheses could be proved, we should only have the satisfaction of knowing that the solar waste of energy by dissipation into space was not dependent entirely upon loss of its sensible heat, but that its existence as a luminary would be prolonged by calling into requisition a limited, though may be large, store of energy in the form of separated matter. The true solution of the problem will be furnished by a theory, according to which the radiant energy which is now supposed to be dissipated into space and irrecoverably lost to our solar system, could be arrested and brought back in another form to the sun itself, there to continue the work of solar radiation."

In accordance with this idea, Sir W. Siemens propounded a theory regarding the conservation of the sun's heat, which I will endeavour to explain to you. In order to understand this theory we must suppose that the planetary system is immersed in a rarified atmosphere, consisting mainly of hydrogen, marsh gas, carbonic oxide, water vapour, etc.; that this is no unreasonable assumption is made clear to us by the fact that it has been proved by Maxwell, Clausius, and Thomson that it is impossible to assign a limit to a gaseous atmosphere in space. The nature of this interplanetary atmosphere is, moreover, made known to us by the meteorolites which frequently find their way to the earth; these meteorolites contain gases hidden in their pores, which, being other than oxygen or nitrogen, must, one would think, have been derived from the interplanetary spaces. These gases are those just enumerated. Further proof, if any be needed, of the existence of gaseous matter in interstellar space, is furnished by spectrum analysis, which tells us that the nucleus of a comet contains carbon, hydrogen, nitrogen, and probably oxygen.

Having arrived at a conception of an interplanetary atmosphere, we have next to think of the action of the sun upon it. Let us first investigate the action of any revolving body upon the gaseous medium in which it is placed. (Exp., wheel and candles.)

We thus see that the sun must act like a great fan, projecting the gases from its equator, and drawing them in at its poles.

Let us think of the stream of hydrogen, oxygen, marsh gas, etc., arriving near the sun at its poles; the rise of temperature will evidently bring about combustion, with its accompanying great development of heat. The result of the combustion, the aqueous vapour and the carbon dioxide, will flow to the solar equator, and be projected into space. Thus it would appear that the constitution of the interplanetary atmosphere would be gradually altered; but Sir W. Siemens here steps in with the suggestion that the solar radiation would bring back the combined materials to their original condition of separation, thus enabling them again to flow towards the sun, and by their second combustion supply the central power with further energy. It remains to show how this could take place.

There is no fact better known to students of chemistry than the decomposition of substances by heat. Nearly all organic substances and many metallic salts are resolved into simple compounds by exposure to heat, while such stable bodies as the metallic oxides, and even water itself, are broken up at a high temperature. The explanation of this very general phenomenon is as follows:-The substances are made up of particles, which are all exactly alike, and all complex, being themselves formed by an aggregation of atoms. These atoms, within the particle or molecule, are subject to definite periodical motions or vibrations, which increase in amplitude with the temperature. It is therefore evident that, as the motions of the atoms within the molecule gradually increase in violence, the time must arrive when the cohesive forces which hold them together must be overcome, and the atoms flying off in different directions will either remain at large, or will come into contact with others derived from other particles, forming, in the majority of cases, simpler aggregations. The destruction of the particles is, in fact, not unlike that of a fly-wheel which is rotated more and more rapidly, until at length the centrifugal force overcomes the cohesion of the iron, and the wheel flies to pieces.

Now, it has been shown by Tyndall and others, that vapour of water and other gaseous compounds possess a remarkable power of absorbing the vibrations of radiant heat, the violence of the atomic vibrations becoming thereby greatly augmented. Nevertheless, under ordinary circumstances, no decomposition is apparent. At low pressures, however, the decomposition is greatly increased, and it is reasonable to suppose that, at the extremely low pressure which reigns in the interplanetary spaces, the destruction of the molecules would be considerable.

Here, then, we have an hypothesis which explains how the solar radiant energy is not lost, but gathered up by the particles of matter distributed in space, to be poured again into the sun by the great gaseous current which circulates among the planets.

Let me, in conclusion, sum up the main conditions of this hypothesis :

(1.) That aqueous vapour and carbon compounds are present in stellar or interplanetary space.

(2.) That these gaseous compounds are capable of being dissociated by radiant solar energy while in a state of extreme attenuation.

(3.) That these dissociated vapours are returned to the sun, and exchanged for recombined vapours by the centrifugal action of the sun.

As Sir W. Siemens has remarked: "If these conditions could be substantiated, we should gain the satisfaction that our solar system would no longer impress us with the idea of prodigious waste through dissipation of energy into space, but rather that of well-ordered, self-sustaining action, capable of perpetuating solar radiation to the remotest future."

VI. CHEMISTRY.

ART. LXI.-On a New Mineral (Awaruite) from Barn Bay.
By W. SKEY.

[Read before the Wellington Philosophical Society, 21st October, 1885.] On the 28th of September two samples, marked Nos. 1 and 2, were transmitted to the laboratory through the Secretary for Mines, as having been obtained by some alluvial miners working near Jackson's Bay, and given by them to the Warden. No. 1 of these parcels, supposed by the contributors to be impure platina, was found not to contain any platina, and to consist entirely of a pure alloy of nickel, iron, and cobalt, in the form of small nuggetty and water-worn grains or scales, perfectly malleable, of a hardness of about 5 and sp. gr. 8.1. Some of these grains have a little lustre, but most of them are dull, owing to a coating of reddish or greenish red oxides. These grains do not reduce copper from its cupreous sulphate, acidulated with muriatic acid. The following is its composition:

Its formula is 2 N + Fe. It is remarkable for the high pro portion of nickel therein. The richest natural alloy of nicke of which I can find any notice is Oktibehite, from the United States of America; it is Ni + Fe, according to which formula there is 51.22 per cent. of nickel present. This alloy (Oktibehite) is of terrestrial origin. Meteoric iron does not often go more than 10 per cent., with a maximum of 20 per cent.; it generally contains carbon.

The New Zealand alloy is undoubtedly of terrestrial origin, and should be found in some basic rock in the vicinity of Barn Bay. The even size of the grains, and their number, together with their richness in nickel and apparent uniformity of composition, support the "terrestrial" theory. The inability of

* This has all been set free from combination with one or other of these metals.