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Page:Popular Science Monthly Volume 8.djvu/329

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PRINCE RUPERT'S DROPS.

according to the theory of evolution, it is related by an unbroken line of descent—granting that we are, if possible, still less able to picture in imagination the process of change from any one form to another—what then? Not surely that the theory of evolution is false! For the same argument will prove that no man present can possibly be the son of his father. Our ignorance is very great, but it is not a very great argument.

The other objection, that the creatures could never have lived to acquire their more important instincts, rests on a careless misunderstanding of the theory of evolution. It assumes in the drollest possible way that evolutionists must believe that in the course of the evolution of the existing races there must have from time to time appeared whole generations of creatures that could not start on life from the want of instincts that they had not got. There can be no need to say more than that these unfortunate creatures are assumed to have been singularly unlike their parents. The answer is, that it is not the doctrine of evolution that the bodies are evolved first by one set of causes and the minds are put in afterward by another. This notion is but the still lingering shadow of the individual-experience psychology. As evolutionists, whether we take the more common view and regard the actions of animals as prompted by their feelings and guided by their thoughts, or believe, as I do, that animals and men are conscious automata, in either case we are under no necessity of assuming, in explanation of the origin of the most mysterious instincts, any thing beyond the operation of those laws that we see operating around us, but concerning which we have yet to learn more, perhaps, than we have learned.—Nature.

 

PRINCE RUPERT'S DROPS.
By WILLIAM LEIGHTON, Jr., S. B.

WHEN from fluidity glass is cooled to a solid structure in the ordinary temperature of the atmosphere, it is found to be very brittle or liable to fracture.

If the glass is so shaped as to be of unequal thickness in its different parts, it can seldom be cooled without fracture, and, if unbroken when cool, is liable to fracture with any subsequent change of temperature or by a sudden jar. Often this fracture takes place, in articles of considerable thickness, with an explosive force, perhaps breaking the glass into a thousand pieces. When glass breaks in this manner, it is said to "fly."

In order to prevent such liability to "fly," glass-ware is annealed.

The process of annealing glass consists in reducing its temperature more slowly than would occur in the air at ordinary temperatures.