620 EVOLUTION OF HEAT, LIGHT, AND ELECTRICITY. 



by Captain Back at 70, or 102 below the freezing point. In both cases, 

 the effect of the atmospheric temperature on the body is greatly influenced by 

 the condition of the air as to motion or rest; thus, every one has heard of the 

 almost unbearable oppressiveness of the "sirocco," or hot wind of Sicily and 

 Italy, the actual temperature of which is not higher than has often been ex- 

 perienced without any great discomfort, when the air is calm : and, on the 

 other side, it may be mentioned that, in the experience of many Arctic voyagers, 

 a temperature of 50 may be sustained, when the air is perfectly still, with 

 less inconvenience than is caused by air in motion at a temperature fifty degrees 

 higher. 1 This is quite conformable to what might be anticipated on physical 

 principles. 



654. Again, the degree of moisture contained in a heated atmosphere makes 

 a great difference jn the degree of elevation of temperature, which may be sus- 

 tained without inconvenience. Many instances are on record, of a heat of from 

 250 to 280 being endured in dry air for a considerable length of time, even 

 by persons unaccustomed to a particularly high temperature ; and persons whose 

 occupations are such as to require it can sustain a much higher degree of heat, 

 though not perhaps for any long period. The workmen of the late Sir F. 

 Chantrey were accustomed to enter a furnace in which his moulds were dried, 

 whilst the floor was red-hot, and a thermometer in the air stood at 350; and 

 Chabert, the "Fire-king," was in the habit of entering an oven whose tempera- 

 ture was from 400 to 600 . 2 It is possible that these feats might be easily 

 matched by many workmen who are habitually exposed to high temperatures ; 

 such as those employed in Iron-foundries, Grlass-houses, and Gas-works. In all 

 these instances, the dryness of the air facilitates the rapidity of the vaporization 

 of the fluid, whose secretion by the Cutaneous glandulse is promoted by heat 

 applied to the surface; and the large amount of caloric which is consumed in 

 this change is for the most part withdrawn from the body, the temperature of 

 which is thus kept down. Exposure to a very elevated temperature, however, 

 if continued for a sufficient length of time, does produce a certain elevation of 

 that of the body; as might be expected from the statements already made, in 

 regard to the variation in the heat of the body with changes in atmospheric 

 temperature ( 651). In the experiments of MM. Berger and Delaroche, 3 it 

 was found that, after the body had been exposed to air of 120 during 17 

 minutes, a thermometer placed in the mouth rose nearly 7 above the ordinary 

 temperature; it may be remarked, however, that, as the body was immersed in 



1 The Author has been informed by Sir John Richardson, that in his last Arctic Expedi- 

 tion, whilst at winter quarters, he was accustomed to go from his sitting-room, to the 

 magnetic observatory at a short distance (about an ordinary street's bi'eadth), without 

 feeling it necessary even to put on a great-coat ; although the temperature of the former 

 was about 50, and that of the air through which he had to pass to the latter was 50, 

 the difference being 100. This immunity from chilling influence was chiefly attributable 

 to the dryness and stillness of the atmosphere; but it is worthy of note that Sir J. R. and 

 the whole of his party on this expedition, abstained entirely from alcoholic liquors; and 

 the Author has received his personal assurance, that his experience on this occasion fully 

 bore out his previous conviction, that continued severe cold is much better borne without 

 recourse to these liquors, than under the employment of them. 



2 The wonderful feats performed by many individuals from time to time of dipping the 

 hand into melted lead, laying hold of a red-hot iron, &c. have been recently shown by 

 M. de Boutigny to be explicable upon very simple principles. For in all such cases, a 

 thin film of aqueous fluid in the "spherical state" intervenes between the skin and the 

 heated surface ; and a hand which is naturally damp, or which has been slightly moistened, 

 may be safely passed into the stream of molten iron as it flows from the furnace ; as was 

 demonstrated by M. de Boutigny at the recent meeting of the British Association at Ips- 

 wich (1851). 



3 " Experiences sur les Effets qu'une forte Chaleur produit sur 1'Economie;" Paris, 

 1805: and "Journal de Physique," tomes Ixiii., Ixxi., et Ixxvii. 



