ANNIVERSARY ADDRESS OF THE PRESIDENT, lix 



would, doubtless, require us to go back into the past some such im- 

 mense period as this to arrive at the epoch when the superficial 

 temperature should have exceeded its present amount by even one or 

 two degrees. At the same time the rate of increase of temperature 

 in descending beneath the surface would be much more rapid than at 

 present. If the superficial temperature amounted to 2° C. above its 

 ultimate limit, instead of being ^\jth of a degree, the rate at which* 

 the temperature would increase in descending would be about sixty- 

 times as great as at present, i. e. there would be an increase of 1° C. 

 for little more than one foot of depth. 



It must be recollected that this state of terrestrial temperature, if 

 due to the cause we are considering, could only have existed at times 

 which, even in a geological sense, must have been extremely remote. 

 The important peculiarity of this state of the earth would seem to 

 consist in the simultaneous existence of a superficial temperature, and 

 therefore of climatal conditions, very nearly the same as at present, 

 with an internal temperature at the depth of a few hundred feet and 

 upwards, immensely greater than at present. If we suppose the pro- 

 cess of sedimentary deposition to have been then going on, we may 

 understand how great an effect might be produced by this internal 

 temperature in the metamorphism of the earlier sedimentary beds. 



The temperature of any point in stellar space is that which would 

 be indicated by a thermometer at that point receiving the heat radi- 

 ating from all the stars composing the universe. The temperature 

 of all bodies must necessarily be affected by this radiation, and in 

 different degrees, according to the positions in space which they may 

 occupy. Hence Poisson was led to adopt the notion that the actual 

 temperature of the earth, whether superficial or internal, is due to • 

 the circumstance of the solar system having passed through a warmer 

 region than that which it now occupies, in the course of that motion 

 by which astronomers generally believe it to be constantly moving 

 from one part of space to another. What may have been the possi- 

 ble effect of this cause in the lapse of indefinite time, it is impossible 

 to say ; but I cannot understand how it could be very considerable 

 without a totally different distribution of the group of stars to which 

 the sun should belong, or the near approach of the solar system to 

 some individual star. The latter hypothesis, however, would be in- 

 consistent with the integrity of the solar system as it now exists, if 

 we . suppose the proximity to any single star to become such as to 

 produce any material modification of terrestrial climate ; and perhaps 

 it may be difficult to conceive how the first hypothesis should escape 

 a similar objection. At all events, it may be regarded as certain, 

 that according to neither of these hypothesis can any considerable 

 effects have been produced by this cause on terrestrial temperature 

 within the later Tertiary period, and that we cannot thus account for 

 the cold of the glacial epoch. 



In considering the influence of the third cause — that of the confi- 

 guration of land and sea — I have endeavoured to ascertain approxi- 

 mately what would be the climatal conditions, more especially in 

 western Europe, in the four following hypothetical cases : — 



