Perhaps the finest illustration of such crystallization is to be found in the deposition of silver from a solution of the nitrate as seen under the microscope. A drop of the solution is placed on a glass slide and while the observer watches it through a low power, a piece of copper wire or, preferably, a minute quantity of the amalgam of tin and mercury, such as is used for "silvering" cheap looking glasses, is brought into contact with it. Chemical decomposition at once sets in and then the silver thus deposited forms one element of a very minute voltaic couple and fresh crystals of silver are deposited upon the silver already thrown down. When the illumination of this object under the microscope is properly managed, the appearance, which resembles that shown in Fig. 18, is exceedingly brilliant, and beautiful beyond description. [Illustration: Fig. 18.] That imagination played strange pranks in the observations of the older microscopists is shown by some of the engravings found in their books. I have now before me a thick, dumpy quarto in which the so-called seminal animalcules are depicted as little men and women, and I have no doubt that, to the eye of this early observer, they had that appearance. But the microscopists of to-day know better. Sir Kenelm Digby, whose name is associated with the Sympathetic Powder, tells us that he took the ashes of burnt crabs, dissolved them in water and, after subjecting the whole to a tedious process, small crabs were produced in the liquor. These were nourished with blood from the ox, and, after a time, left to themselves in some stream where they throve and grew large. Now, although Evelyn, in his diary, declares that "Sir Kenelm was an errant mountebank," it is quite possible that he was honest in his account of his experiments and that he was merely led astray by the imperfection of his instruments of observation. It is more than likely that the creatures which Digby saw were entomostraca introduced in the form of ova which, unless a good microscope be used, are quite invisible. These would develop rapidly and might easily be mistaken for some species of crab, though, when examined with proper instruments, all resemblance vanishes. When let loose in a running stream it would evidently be impossible to trace their identity and follow their growth. But while some of these stories may have originated in errors of observation this will hardly explain some of the statements made by those who have advocated this strange doctrine. Father Schott, in his "Physica Curiosa," gives an account of the resurrection of a sparrow and actually gives an engraving in which the bird is shown in a bottle revived! Although the subject, of itself, is not worthy of a moment's consideration, it deserves attention as an illustration of the extraordinary vagaries into which the human mind is liable to fall. THE POWDER OF SYMPATHY