Professor Buckland's Address. 57 



valve being acted on, or giving sufficient vent for the steam. 

 But this I only mention as one of the various causes to which 

 explosions may be ascribed. 



Since air, whilst it expands by having its temperature raised 

 under a constant pressure, absorbs a considerable portion of 

 latent heat, and still more if the pressure be decreasing, it pro- 

 bably also at same time, like steam, absorbs a corresponding 

 portion of electricity. Now, I presume it is on this principle 

 that we are to seek for an explanation of the economy of the 

 hot-blast furnace. When cold and compressed air is forcibly 

 injected into the fire, the fuel and bricks, being generally 

 bad conductors of electricity, cannot supply it with sufficient 

 promptitude or quantity both for the expansion of the air 

 and for the formation of the gaseous products of the combus- 

 tion. Hence, the process proceeds more languidly than when 

 the air has been previously heated, and supplied with a cor- 

 responding share of electricity. 



Address to the Geological Society, delivered at the Anniversary, 

 on the 2\st of February 1840. By the Rev. Professor Buck- 

 land, D. D., F. R. S., Corresponding Member of the Insti- 

 tute of France, President of the Society.'* 



POSITIVE GEOLOGY. 



Devonian System. — In the Home Department of Positive Geology, the 

 most striking circumstance has been an announcement by Professor Sedg- 

 wick and Mr Murcbison of the conclusion to which they were led by Mr 

 Lonsdale's suggestion in December 1837, founded on the intermediate 

 character of the fossils in the Plymouth and Torbay limestone, — that the 

 greater part of the slate-rocks of the south of Devon and of Cornwall be- 

 long to the old red sandstone-formation. 



The order of the observations which have led to this important result, 

 is nearly as follows : — 



In a paper read at Cambridge, during the winter of 1836-37, Professor 

 Sedgwick considered the fossiliferous slates on both sides of Cornwall to 

 be of the same formation, and coeval, or nearly so, with the calcareous 

 rocks that lie between the slates of South Devon. 



In 183G and 1837 also,t Messrs Sedgwick and Murchison proposed to 



* The biographical pari of the Address is left out, owing to the crowded state of 

 the present number of the Journal. —Edit. 



t In August 183f>, at the Meeting of I lie British Association at Bristol : and in 

 a paper read before the Geological Society, May and June, 1887, now published in 

 the Qeological Transactions, Second Series, vol. v. Pari iii. 



