1853] 



MEETING OF THE BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 



55 



the geolocrist has been able to recognize, some of these higher 

 types had propably no existence at all. 



Each successive discovery, like those which I have mentioned, 

 of the remains of animals ot the higher types in the older rocks, 

 is regarded by some geologists as an addition to the cumulative 

 evidence by which they conceive that the theory of non-progres- 

 sion will be ultimately established ; while others consider the 

 deficiency in the evidence required to establish that theory as far 

 too great to admit the probability of its being supplied by future 

 discovery. Nor can the theory derive present support, it is 

 contended, by an appeal to any properties of inorganic matter, or 

 physical laws, with which we are acquainted. Prof. W. Thom- 

 son has recently entered into some very interesting speculations 

 bearing on this subject, and suggested by the new theory of 

 heat of which I have spoken. The heat of a heavenly body placed 

 under the same conditions as the sun, must, it has been said, be 

 ultimately exhausted by its rapid emission. This assertion 

 assumes the matter composing the sun to have certain properties 

 like those of terrestrial matter with respect to the generation and 

 emission of heat; but Prof. Thomson's argument places the sub- 

 ject on better grounds, admitting, always, the truth of the new 

 theory of heat. That theory asserts, in the sense which I have 

 already stated, the exact equivalence of heat and motive power; 

 and that a body, in sending forth heat must lose a portion of that 

 internal motion of its constituent particles on which its thermal 

 state depends. Now we know that no mutual action of these 

 constituent particles can continue to generate motion which might 

 compensate for the loss of motion thus sustained. This is a 

 simple deduction from dynamical laws and principles, independent 

 of any property of terrestrial matter which may poss'bly distin- 

 guish it from that of the sun. Hence, then, it is on these 

 dynamical principles that we may rest the assertion that the sun 

 cannot continue for an indefinite time to emit the same quantity 

 of heat as at present, unless his thermal energy be renovated from 

 some extraneous source. The same conclusion may be applied to 

 all other bodies in the universe which, like our sun, may be 

 centres of intense heat; and, hence, reeogniziufr no adequate 

 external supplies of heat, to renovate these existing centres of 

 heat, Prof. Thomson concludes that the dispersion of heat, and 

 consequently of physical energy, from the sun and stars into 

 surrounding space without any recognizable means of reconeen- 

 tration, is the existing order of nature. In such case the heat of 

 the sun must ultimately be diminished, and the physical coudition 

 of the earth therefore altered, in a degree altogether inconsistent 

 with the theory of non-progression. 



Mr. Rankine, however, has ingeniously suggested an hypothesis 

 according to which the reconcentration of heat is conceivable. 

 Assuming the physical universe to be of finite extent and sur- 

 rounded by an absolute vacuum, radiant, heat (supposing it to be 

 propagated in the same way as light) would be incapable of 

 passing into the vacuum, and would be reflected back to foci 

 corresponding to the points from which it emanated. A recon- 

 centration of heat would thus be effected; and any of the heavenly 

 bodies which had previously lost their heat, might, on passing 

 through these foci, be rekindled into bright centres of radiant 

 heat I have alluded more particularly to this very ingenious, 

 though, perhaps, fanciful hypothesis, because some persons have, 

 I believe, regarded this view of the subject as affording a sauction 

 to the theory of non-progression; but even if wo should admit 

 its truth to the fullest extent, it may be deemed, I think, entirely 

 inconsistent with that uniformity and permanence of physical 

 condition in any of the heavenly bodies which the theory just 

 mentioned requires in our own planet. The author of this 

 hypothesis did not possibly contemplate any such application of 

 it; nor am I aware how far he would advocate it as really 



applicable to the actual constitution of the material universe, or 

 would regard it as suggesting a possible and conceivable, rather 

 than a probable, mode of counteracting the constant dispersion of 

 heat from its existing centres. He has not, 1 think, attempted to 

 work out the consequences of the hypothesis as applied to light, — 

 to which it must, 1 conceive, be necessarily considered applicable 

 if it be so to heat. In such case the foci of the reflected heat 

 would be coincident with those cf the reflected light, proceeding 

 originally from the same luminous bodies. These foci would thus 

 become visible as the images of stars ; so that the apparent number 

 of stars would be constantly increasing with the increasing num- 

 ber of images of each star produced by successive reflexions. 

 This will scarcely be considered the actual order of nature. It 

 would be easy to trace other consequences of the application of 

 this hypothesis to light; but I would at present merely state that 

 my own convictions entirely coincide with those of Prof. Thomson] 

 If we are to found our theories upon our knowledge, and not 

 upon our ignorance of physical causes and phenomena, 

 I can only recognize in the existing state of things a passing 

 phase of the material universe. It may be calculated in all, 

 and is demonstrably so in. some respects, to endure under the 

 action of known causes, for an inconceivable period of time ; but 

 it has not, I think, received the impress of eternal duration in 

 characters which man is able to decipher. The external tempera- 

 ture any physical conditions of our own globe may not, and pro- 

 bably cannot, have changed in any considerable degree since the 

 first introduction of organic beings on its surface ; but I can still 

 only recognize in its physical state during all geological periods, 

 a state of actual though exceedingly slow progression, from an 

 antecedent to some ultimate state, on the nature of which our 

 limited powers will not enable us to offer any conjecture founded 

 on physical research. The theories, even, of which 1 have been 

 speaking, may probably appear to some pei-sons as not devoid of 

 presumption; but for many men they will ever be fraught with 

 deep speculative interest: — and, let me add, no charge of pre- 

 sumption can justly lie against them if entered upon with that 

 caution and modesty which ought to guide our inquiries in these 

 remote regions of physical science. 



I feel how imperfect a view I have now submitted to you of 

 recent scientific proceedings. I have given no account of the 

 progress of Chemistry, of Practical Mechanics, or of the sciences 

 connected with Natural History ; nor have I spoken of Ethnology, 

 a science which, though of such recent date, is become of great 

 interest, and one which is occupying the minds of men of great 

 learning and profound research. I can only hope that the chair 

 which 1 have now the honor to occupy, will be henceforth filled 

 by men qualified to do full justice to these important branches 

 of science. I trust that what I have said, however, will convey 

 to you some idea of the activity which pervades almost every 

 department of science. 



I must not conclude this Address without some mention of 

 what appear to me to be the legitimate objects of our Association 

 — nor without some allusion to circumstances calculated, I think, 

 to give increased importance to its general working and influence. 



There are probably few amongst us of whom the inquiry has 

 not been made — after any one of our meetings — whether any 

 striking discovery had been brought forward '(■ — and most of us 

 will also probably have remarked that an answer in the negative 

 has frequently produced something like a feeling of disappoint- 

 ment in the inquirer. But such a feeling can arise only from a 

 misapprehension of what I conceive to be the real and legitimate 

 objects of the British Association. Great discoveries do not re- 

 quire associations to proclaim them to the world. They proclaim 

 themselves. We do not meet to receive their announcement, or 



