excellent results are obtained. It is a singular fact that almost every snow crystal differs in some particular from all others collected. Mr. Bentley, of Nashville, Vermont, has doubtless given more attention to snow crystal photography than any one else, and the number of different forms which he has already obtained is remarkably large, and many of them are exquisite. Much has also been done on questions relative to the crystalline structure of various minerals by the aid of the microscope, as for example, 'Inclusions of Petroleum in Quartz' (Jour. Am. Chem. Soc.) 20: 795, and also concerning the 'Solution Vein Theory' for the origin of gold. In the same way it is possible that in the future a unanimity of opinion may be produced concerning the crystallization of iron, which is worthy of serious attention as the enormous amount of that metal used in construction increases year by year.
|Fig. 20. Cow Hair, 2,200 Diameters||Fig. 21. Cross Section of Horn of African Rhinoceros, x 60 Diameters. Polarized Light.|
The value of the part which the microscope plays in determining facts about the minute structure of the animal organisms can scarcely be overestimated. The bacteriological analysis of water in connection with zymotic diseases; the determination of disease germs in impure air; the examination of useful and injurious bacteria in food; all this and more must be credited to the microscope in the development of medical science and sanitation.
A detailed description of all the applications of photomicrography to nature study can not well be given here, and so a few of the important ones only have been briefly noticed. The chief value of it all seems to be the aid rendered in the dissemination of knowledge. To attempt to look beneath the superficial and discover the ulterior is a fundamental desire in the active, civilized mind. Since the beginning of the seventeenth century, when Galileo was imprisoned for stating his belief in the motion of the earth, we look with pride at the development of science