SCIENTIFIC KNOWLEDGE IN LARGE TOWNS. 93 



face, in preparing itself for crystallization, expands, and becomes 

 lighter than that which is below it ; in consequence of which it re- 

 mains at the surface, and being a bad conductor of heat, it preserves 

 the deep water in large rivers, lakes, and seas from being frozen. 

 From the same source we learn that the suddenness of the transi- 

 tion from heat to cold, and the converse, which might be expected 

 to take place during sudden frosts and thaws, and which would prove 

 greatly injurious to our health,is moderated by the latent heat of fluid- 

 ity being given out by the water as it crystallizes into ice, and being 

 re-absorbed when it returns to a state of liquefaction. In the Polar 

 regions, where it is necessary to the existence of the animals who 

 inhabit them that their internal heat should be kept as much as 

 possible from radiating to the surrounding cold substances, we find 

 them provided with skins of such colours and materials as are most 

 opposed to the passage of caloric ; and the breasts of aquatic birds, 

 which in swimming are constantly exposed to the action of fresh 

 particles of cold water, are defended by thick down, which, owing 

 to the extreme fineness of its feathers, proves almost a perfect non- 

 conducting substance, and thus opposes a strong barrier to the ab- 

 straction of heat from the body. It is thus that Science, in unra- 

 velling the mysteries of Nature, unfolds to our view the wisdom, 

 power, and goodness of the Almighty Creator. The harmony of 

 nature is not the least extraordinary part of this view. The different 

 phenomena seem to arise one out of the other, and to keep each 

 other in equilibrio. The grand miracle is the formation of Nature ; 

 the framing of that universal machine which regalates itself accord- 

 ing to certain fixed laws that have been appointed for it. A watch 

 of ordinary construction is a surprising and beautiful piece of me- 

 chanism, but with every great change of temperature it requires the 

 regulating fingers of its owner. But there are others in the con- 

 struction of which the principle of the unequal expansion of different 

 metals by heat has been so introduced, that they regulate themselves, 

 and will record the time in the course of a whole year to within 

 half a second. Now, supposing by means of such a chronometer, we 

 had, under very perilous circumstances at sea, been enabled to cal- 

 culate our distance from land, and steer our course with such nicety 

 as to escape an almost inevitable danger, should we not be constantly 

 talking of this instrument, exhibiting and explaining its construc- 

 tion to our friends, and referring to its maker as being, under Pro- 

 vidence, the protector of our lives ? Just so, with the same zeal, I 

 mean, and in the same spirit, are we bound to unlock the book of 

 Nature with the key of Science, and to circulate its truths far and 



