ADDRESS. Ilif 



buted. The theory of non-progression, on tlie contrary, recognizes no primi- 

 tive state oF our planet differing essentially from its existing state ; the 

 only changes it does recognize being those which are strictly periodical, and 

 therefore produce no permanent alteration in the state of our globe. With 

 reference to organic remains, the difference between these theories is exactly 

 analogous to that now stated with reference to inorganic matter. The theory 

 of progression asserts that there has been a general advance in the forms of 

 organic life, from the earliest to the more recent geological periods. This 

 advance must not be confounded, it should be observed, with that progressive 

 development, according to which animals of a higher organic structure are 

 but the improved lineal descendants of those of tiie lowest grade, thus abo- 

 lishing all distinction of species. It is merely meant to assert that the higher 

 types of organic being are far more generally diffused at the present time, 

 and far more numerous and varied, than they were at the earlier geological 

 periods ; and that, moreover, at the earliest of those periods which the geo- 

 logist has been able to recognize, some of these higher types had probably 

 no existence at all. The theory of non-progression does not recognize the 

 gradual advance here spoken of. 



Each successive discovery, like those I have mentioned, of the remains of 

 animals of the higher types, in tiie older rocks, is regarded by some geolo- 

 gists as an addition to the cumulative evidence by which they conceive that 

 the theory of non-progression 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 disco- 

 very. 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. Professor W. Thomson 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. Tliis assertion assumes tlie matter com- 

 posing the sun to have certain properties like those of terrestrial matter with 

 respect to the generation and emission of heat ; but Professor Thomson's 

 argument places the subject 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 possibly distinguish 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 reno- 

 vated 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 in- 

 tense heat ; and hence, recognizing no adequate external supplies of heat to 

 renovate these existing centres of heat. Professor Thomson concludes that 

 the dispei'sion of heat, and consequently of physical energy, from the sun 

 and stars into surrounding space without any recognizable means of recon- 

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

 must ultimately be diminished, and the physical condition of the earth there- 



