230 
DR. TYNDALL ON MOLECULAR INFLUENCES. 
bad conductor-much inferior, indeed, to wood in the direction of the fibre. Doubtless 
this conduces to the animal’s comfort. Exposed to the rays of a tropical sun, if these 
huge bony masses were capable of assuming a high temperature during the day and 
losing it again at night, it must be a source of the greatest inconvenience to the 
animal, as at present constituted. The horns of the Rhinoceros and Cow, however, 
still more strikingly exemplify that fitness of parts which is perpetually presented to 
the student of natural science. In the latter case especially, the mass of horn in close 
contact with the skull, and therefore capable of transmitting heat directly to the 
animal’s brain, must be attended with very unpleasant consequences, if horn were a 
good conductor. Given such a constitution, the substance fixed upon by om' o™ 
^lightened intellect to furnish the animal with such weapons of defence, would be 
just such as nature has chosen. , 
As a general rale, sudden changes of temperature are prejudicial to animal and 
vegetable health ; the substances used in the construction of organic tissues are 
exactly such as are best calculated to resist those changes. Coal enters largely into 
the composition of such tissues, and it is an exceedingly bad conductor. 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 mannei. It i^ 
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 . . . 0 
Sole leather ^ 
Bees’-wax . 0 
Glue produces a deflection of 0 
Gutta-percha 0 
India-rubber ^ 
Filbert-kernel ® 
Almond-kernel ^ 
Boiled ham-muscle 
Raw veal-musele ^ 
The substances here named are all of them animal and vegetable productions ; and 
the experiments demonstrate the extreme imperviousness of every one of them. 
Starting from the principle that sudden accessions or deprivations of heat are preju- 
dicial to animal and vegetable health, we see that the materials chosen are precisely 
