HEAT CONDUCTION. 



a round-faced hammer, and placed upon a red- 

 hot piece of iron which will maintain its supply 

 of heat. 



2. Dipping the Hand into Molten Lead. 



It has been credibly stated that our present 

 king, on one of his visits a long time ago to our 

 seats of industry, had the courage to dip his 

 hand into a vessel of molten lead. Whether 

 this be true or not, the experiment is one which 

 can be, and has not rarely been, performed with- 

 out injury. 



Water boils at 212 F., and if the hand were 

 dipped for the briefest moment into boiling 

 water, the result would be terrible pain and 

 the most serious injury. The temperature at 

 which lead melts is 400 degrees higher than 

 that of boiling water. How is it that contact 

 with it can be less dangerous ? 



The explanation is very much like that 

 given in the last section, of the spheroidal state 

 of water. 



The heat of the lead vaporises the moisture 

 in the skin, turning it into a kind of glove of 

 steam-gas, which is a very bad conductor of 

 heat, so that the heat of the lead is not very 

 rapidly conducted to the skin. The skin it- 

 self has an outer insensitive portion which can, 

 without pain, sustain excessive heat for a very 

 short time, before its conduction through to 



155 



