296 



THE GEOLOGIST. 



material. The thermal portion of space must therefore be material that 

 is occupied by matter. There can be no absolute void or pure space be- 

 tween us and any visible star, no matter how remote ; even though its dis- 

 tance be so immense that the courier ray that now announces to our senses 

 its existence, may have started on its errand thousands of millions of years 

 ago, travelling all that time at the rate of a hundred and seventy thousand 

 miles a second, still in the immense, the inconceivable space so run over 

 by the luminous messenger, no absolute void could have existed, otherwise 

 the star must be invisible to us. 



Mr. Mackie is therefore right in stating "that if heat be confined to 

 matter, how can we speak of hot and cold regions of space ? " but he 

 should have added pure or empty space where no matter exists, as I only 

 meant those portions of space occupied by matter surrounded by and float- 

 ing in a thermal ocean ; for whether heat be a fluid or a wave, we cannot 

 expect to find the causes of telluric changes of temperature by travelling 

 into regions of space where nothing exists, where there is no entity but 

 nought, " where death is life." Mr. Mackie says (last number of ' Geo- 

 logist'), "if the sun moves on with his surrounding worlds, these will all 

 travel onwards together in the same ethereal material envelope ; and there- 

 fore, unless the supposed hot and cold regions of space have temperatures 

 of much higher or much lower degrees than the general temperature of 

 the solar region, the effect would be imperceptible.'" It is evident that 

 the portions of space so traversed by our solar system at the rate of 57^ 

 miles a second, moving towards the constellation Hercules, must be ma- 

 terial, for so far as we can see any object in the universe, between us and 

 that object there can be no absolute void or pure space, otherwise it must 

 be invisible. Now it is clear that the regions of space occupied by matter 

 cannot be of the same temperature, as the causes that generate light and 

 heat are neither uniform in intensity nor distance. The path traversed by 

 our solar system in space therefore cannot be isothermal. 



It is not likely that our solar system is travelling through space sur- 

 rounded by the same ethereal envelope, as Mr. Mackie seems to think, for 

 this would be, supposing that outside this ethereal envelope nothing ex- 

 isted but pure space, an assumption quite opposed to the facts and reasons 

 already stated. Besides, whether heat be a fluid or a wave, in either case 

 it must be subject to the ordinary influences of physical agencies ; there- 

 fore the same condition of matter constituting uniformity of temperature 

 could not follow and surround our solar system in its travels through 

 space. 



David Leslie, M.D. 



Tunbridge, July 19^, 1863. 



The Portland Fissures. 



Sie, — I hope you will allow me to correct a mistake which you have 

 made in your remarks on my last letter, in sa} 7 ing that my theory was 

 that of " the deposition of the extinct animals in caves before the caves 

 existed." On the contrary, I said that I was of opinion that all bone- 

 caves were only formed by the animal remains embedded in the limestone 

 deposit before its consolidation, and, consequently, before the existence of 

 any caves in it. 



The question with respect to the Portland and Oreston fossils is en- 

 tirely dependent on the truth of certain facts. First, with respect to 

 the Portland fossils, can the statement of Captain Manning, of the ' Willis's 



