364 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



with bodies which are good or bad conductors causes a sensation of 

 cold or of heat, because the exchange of heat which takes place in one 

 direction or the other between these bodies and our skin is more or 

 less rapid. The disagreeable feeling which arises from a scald is due 

 to a too rapid exchange of heat bringing about the disorganization of 

 the tissue. The same feeling may result from contact with an object 



which has a very low tem- 

 perature, such is the feeling 

 experienced on touching a 

 piece of frozen mercury. 

 In polar climates, the hand 

 must not be allowed to 

 touch metallic objects, 

 which must be enveloped 

 in cloth, or else thick gloves 

 must be used. 



The feeble conductivity 

 of certain substances, such 

 as wood and felt, has been 

 put to a curious domestic 

 use. 



The automatic stewpan, 

 which was shown in the 

 Paris Exhibition of 1867, 

 and which is in use in 

 the northern parts of 

 Europe, is nothing else than 

 FIG. 249. Automatic stewpan. a metal stewpan, into 



which the meat, vegetables, 



and all other ingredients of the stew, including water, is placed. 

 The whole is put on the fire till it boils. The stewpan is then 

 inclosed in a box that has the inside and lid lined with a thick layer 

 of felt. The stewpan is also covered with a pad of the same material . 

 it is closed hermetically and the utensil is then left to itself. The 

 cooking continues, and is completed without fire, because, owing 

 to the very feeble conductivity of the envelope, the heat within 

 maintains a very high temperature for many hours ; at the end of three 

 hours it will have gone down, on an average, not more than 12 C. 



