Page:Popular Science Monthly Volume 10.djvu/509

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together with great rapidity in virtue of their wonderful elasticity. If we assume that this motion takes place in accordance with the well-known laws of the diffusion of gases, the theory gives a satisfactory explanation of all well-established electrical phenomena.

In the autumn of 1872 Prof. Cooke delivered an interesting and important course of lectures on the "New Chemistry," which was subsequently published in the "International Scientific Series." His volume is one of the best and most successful of these books, and has been very highly appreciated both in this country and abroad, having been translated into most of the languages of Europe.

Among Prof. Cooke's lesser scientific publications may be mentioned the following:

1. "On the Relation between the Atomic Weights of the Chemical Elements" ("Memoirs of the American Academy," vol. v., 1854).
It was first shown in this paper that when the elementary substances are classified in natural groups, their atomic weights and other physical qualities are related by regular differences.
2. "On Two New Crystalline Compounds of Zinc and Antimony, and on the Cause of the Variation of Composition observed in their Crystals" ("Memoirs of the American Academy," vol. v., 1855).
This investigation proved that the crystalline form of these compounds was preserved under very considerable variations of composition, and indicated that the excess of one or the other constituent depended not solely on the composition of the menstruum in which the crystals were formed, but also on the chemical force which determines the union of the elements in definite proportions. The subject was still further discussed in the following paper, published during a visit to England.
3. "Crystalline Form not necessarily an Indication of Definite Chemical Composition, or on the Possible Variations of Composition in a Mineral Species independent of the Phenomena of Isomorphism" (Philosophical Magazine for June, 1860).
4. "On the Dimorphism of Arsenic, Antimony, and Zinc" (American Journal of Science for March, 1861).
It was here proved that all three of these elements are capable of crystallizing in octahedrons of the regular system.
5. "On Octahedral Galena" (American Journal of Science for January, 1863).
In this it was shown that the octahedral cleavage in this singular variety of galena from Lebanon County, Pennsylvania, is merely an unusual development of a constant condition.
6. "Crystallographic Examination of the Hebron Childrenite, and Comparison of this Variety with the Childrenite of Tavistock" (American Journal of Science for September, 1863).
7. "Crystallographic Examination of the Acid Tartrates of Cæsia and Eubidia" (American Journal of Science for January, 1864).