112 THE MECHANICAL FUNCTIONS. 



which adapt themselves to their various changes of 

 form and to their different movements. The ball 

 of the eye obtains a similar protection by resting 

 on a mass of fat, which occupies the remaining 

 space at the bottom of the orbit, and facilitates the 

 quick and sudden movements required of that 

 organ. The same design is apparent in the gra- 

 nules of fat which occur in the cavities of most of 

 the joints, and which being interposed between the 

 terminal cartilages, limit their extent of contact, 

 diminish their friction, and by equalizing the pres- 

 sures facilitate their relative motion. 



In warm-blooded animals, the fat which forms a 

 layer underneath the skin is of great use in pre- 

 venting the rapid dissipation of warmth, being itself 

 a very slow conductor of heat. All the Cetacea 

 derive considerable protection from cold, by the 

 great thickness of this subcutaneous layer. 



§ 5. Muscular Power. 



In Machines contrived by human skill, the chief 

 art consists in devising expedients for regulating 

 and directing the given moving power, so that it 

 may bear, in the proper degree, and in the proper 

 order, upon some assigned objects, and produce 

 some particular effect. The whole of the apparatus 

 employed with this intention, however numerous 

 may be its parts, however various the forms of its 

 wheels, its levers, or its pulleys, and however com- 

 plicated may be their connexions, resolves itself 

 into a series of intermediate instruments for trans- 

 ferring motion from the source of power, or the 



