~36 Intelligence and Miscellaneous Articles, 



that he had verified the correctness of the node in the first period 

 from other observations, but he had not succeeded in finding obser- 

 vations corresponding in date with those of the latter period. 

 The paper is followed by eight sheets of curves, as follows : — ■ 



I. Diurnal Curves of combination of Declination and Horizontal 



Force. 



(1) Mean of all the days in each year (separately), 1841-1847. 



(2) Mean of all the days in each year (separately), 1848-1857. 



(3) Mean of all the days in the aggregate of the same nominal 

 months (separately) through the period 1841-1847. 



(4) Mean of all the days in the aggregate of the same nominal 

 months (separately) through the period 1848-1857. 



II. Diurnal Curves of Vertical Force. 



(5) Mean of all the days in each year (separately), 1841-1847. 

 (0) Mean of all the days in each year (separately), 1849-1857. 



(7) Mean of all the days in the aggregate of the same nominal 

 months (separately) through the period 1841-1847. 



(8) Mean of all the days in the aggregate of the same nominal 

 months (separately) through the period 1849-1857. 



XLIL Intelligence and Miscellaneous Articles. 



ON THE EARTH'S CLIMATE IN PALEOZOIC TIMES. 



To Dr. John Tyndall, F.R.S., 8>c. 

 My dear Sir, Montreal, February 1, 1864. 



TNa Note which appeared in the Philosophical Magazine for October 

 -■- 1863 (page 323), I endeavoured to explain the warmer climate 

 of the earth in palaeozoic times by the aid of your remarkable re- 

 searches on radiant heat, by which you have shown that small quan- 

 tities of various gases, when diffused in the atmosphere, greatly 

 retard cooling by radiation. I suggested that the large amount of 

 carbon which w r as then diffused in the atmosphere as carbonic acid, 

 and which has since been separated in the forms of carbonate of lime 

 and carboniferous matters, must have had a powerful influence upon 

 the temperature of the earth's surface during the palaeozoic period ; 

 I also indicated the influence of marsh-gas from the decay of the 

 abundant vegetation of the period. I was not at the time aware 

 that my suggestions had been anticipated by you in the Bakerian 

 Lecture for 1861, where you say that, from its influence on terrestrial 

 radiation, all variation in the amount of aqueous vapour in the atmo- 

 sphere must produce changes in climate; and you then add, " Similar 

 remarks would apply to the carbonic acid diffused through the air, 

 while an almost inappreciable admixture of any of the hydrocarbon 

 vapours would produce great effects on the terrestrial rays, and cor- 

 responding changes of climate. It is not, therefore, necessary to 

 assume alterations in the density and height of the atmosphere to 

 account for different amounts of heat being preserved to the earth at 

 different times ; a slight change in its variable constituents w r ould 



