THE KEJUVENESCENCE ()E (HrVSTALS.* 



By Prof, John W. Jidd, F. M. S, 



Very soon after tlie invention of tlie niicrosoo])e tlie value of that in 

 strnuieiit in investigating tlie i)lieiionu'na of crystallization began to be 

 recognized. 



The study of crystal morphology and crystallo-genesis was initiated 

 in this country by the observations of Robert Boyle; and siuee his day 

 a host of investigators — among whom may be especially mentioned 

 Leenwenhoek and Vogelsang in Holland, Link and Frankenheim in 

 Germany, and Pasteur and kSeuarmont in France — have added largely 

 to our knowledge of the origin and development of crystalline struc- 

 tures. Nor can it be said with justice that this field of investigation, 

 opened up by English pioneers, has been ignobly abandoned to others, 

 for the credit of British science has been fully maintained by the nu- 

 merous and brilliant discoveries in this department of knowledge by 

 Brewster and Sorby. 



There is no branch of science which is more dependent for its prog- 

 ress on a knowledge of the phenomena of crystallization than geology. 

 In seeking to explain tlie complicated phenomena exhibited by the crys- 

 talline masses composing the earth's (;rust, the geologist is constantly 

 compelled to appeal to the physicist and chemist; from them alone can 

 he hope to obtain tht; light of experiment and the leading of analogy 

 wher(?by he may hope to solve the ])rol)lems which confront him. 



J>ut if geology owes much to the researches of those physicists and 

 chemists who have devoted their studies to the i)li('nomena of crystalli- 

 zation, the debt has been more than re[)ai(l through the new light 

 which has been thrown on these (questions by the in\-estigations of nat- 

 urally formed crystals by mineralogists and geologists. 



In no class of physical oi»erations is time such an important factor as 

 in crystallization, and Xature, in in'oducing her inimitable exam]>les of 

 crystalline bodies, has been unsi)aring in her expenditure of time. 

 Hence it is not surprising to find that some of the most wonderful i)he- 

 nomeua of crystallization can best be studied — some indeed can only 

 be studied — in those exquisite specimens of Nature's handiwork which 



*Tlie Friday evening discourse, delivereil at tlie Koyal Institution on January 30, 

 1891. (From Xafiire, Mav28, 1891; vol. xi.n', i)p. 83-8(3.) 



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