SKETCH OF PROFESSOR J. P. COOK, Jr. 493 



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 satis- 

 factory 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 men- 

 tioned the following:: 







1. " On the Relation between the Atomic Weights of the Chemical Ele- 

 ments " (" 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 composi- 

 tion of the menstruum in which the crystals were formed, but also on the chemi- 

 cal 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 develop- 

 ment of a constant condition. 



6. " Crystallographic Examination of the Hebron Childrenite, and Compari- 

 son of this Variety with the Childrenite of Tavistock " {American Journal of 

 Science for September, 1863). 



7. "Crystallographic Examination of the Acid Tartrates of Csesia and 

 Eubidia" (American Journal of Science for January, 1864). 



