Dr. Tyndall on Molecular Influences. 137 



ductor. Here are the deflections obtained with three different 

 descriptions of this substance : — 



o 



Sunderland coal ... 8 

 Boghead cannel ... 8 

 Lesmahago cannel . . 8 



The following results illustrate the subject in a still more 

 striking manner. It is almost needless to remark that each of 

 the substances mentioned was reduced to the cubical form, and 

 submitted to an examination similar in every respect to that of 

 wood and quartz. While, however, a cube of the latter substance 

 produces a deflection of 90°, a cube of 



o 



Sealing-wax produces a deflection of . 



Sole leather 



Bees' -wax 



o 



Glue produces a deflection of .... 



Gutta-percha 



India-rubber 



Filbert-kernel 



Almond- kernel 



Boiled ham-muscle 



Haw veal-muscle 



The substances here named are all of them animal and vege- 

 table productions ; and the experiments demonstrate the extreme 

 imperviousness of every one of them. Starting from the princi- 

 ple that sudden accessions or deprivations of heat are prejudicial 

 to animal and vegetable health, we see that the materials chosen 

 are precisely those which are best calculated to avert such changes. 

 It is yet to be estimated what influence the extreme non-con- 

 ductibility of muscular tissue exerts in producing the remarkable 

 constancy of temperature observed in the human body in different 

 climates. The cuticle is an exceedingly bad conductor, and this 

 explains the insensibility to heat of hands on which the skin has 

 been thickened by exposure. Probably many escapes from the 

 fiery ordeal, which have been hitherto referred to collusion, 

 might be scientifically explained by reference to this fact. While 

 studying at Marburg, I have sometimes heard Professor Bunsen 

 make a good-humoured remark on the tenderness of his pupils' 

 fingers. Accustomed as he was to the manipulation of the glass 

 used in his admirable eudiometrical researches, his fingers had 

 acquired an insensibility to heat sufficient to carry him safely 

 through an ordeal which, in other cases, would undoubtedly 

 invoke the judicial condemnation of the middle ages. The ex- 



