196 Transactions. — Miscellaneous. 



the general atmosphere in and around the pit is so high in 

 temperature. The moment the stone is removed from the 

 oven to a cooler surrounding atmosphere radiation begins 

 to take place more rapidly — -that is, the stone burns more 

 easily a hand or foot in contact with it. 



It is a well-known fact that all these volcanic rocks are bad 

 conductors of heat, and numerous observers have commented 

 upon this. Those who have visited volcanic regions tell us 

 "that the hardened crust of a lava-stream is a bad conductor of 

 heat, consequently when the surface of the mass has become 

 cool enough to be walked upon the red-hot mass may be 

 observed through the rents to lie only a few inches below. 

 Many years, therefore, may elapse before the temperature of 

 the whole mass has fallen to that of the surrounding soil. 

 Eleven months after the eruption of Etna, Spallanzani could 

 see that the lava was red hot at the bottom of the fissures, 

 and a stick thrust into one of them instantly took fire. The 

 Vesuvian lava of 1785 was found by Breislak, seven years 

 afterwards, to be still hot and steaming internally, though 

 lichens had already taken root on its surface. The ropy lava 

 erupted by Vesuvius in 1858, and spread over the surround- 

 ing country, was observed in 1870 to be still so hot even near 

 its termination that steam issued abundantly from its rents, 

 many of which were too hot to allow the hand to be held in 

 them. Hoffmann records that the lava that flowed from 

 Etna in 1787 was still steaming in 1830. But still more 

 remarkable is the case of Jorullo, in Mexico, which poured 

 out its lava in 1759. Twenty-one years later a cigar could 

 still be lighted at its fissures ; after forty-four years it was 

 still visibly steaming; and even in 1846 — that is, after eighty- 

 seven years of cooling — two vapour columns were still rising 

 from it "(n). These stones, therefore, being of igneous 

 origin, are almost certainly very slow in conductivity and 

 also in radiation or cooling, but for actual proof of this one 

 must go further. 



In order to prove, if possible, my theory that this stone 

 does not throw out as much heat, or, in other words, does 

 not burn so severely, as an ordinary stone of different com- 

 position, I have had some experiments conducted at the 

 Otago School of Mines by the Director, Professor Park. I 

 asked him to compare in some way the heat-throwing-off 

 property of this stone with that of others of very different 

 composition, by subjecting them for the same space of time 

 to the same amount of heat and then measuring the respec- 

 tive amounts of heat radiated. I suggested various rough 

 experiments, such as heating the stones from below and 

 having on the upper surface evaporating glasses of water or 

 highly inflammable liquids, &c, in order to prove which 





