A DIVERS ART ADDRESS OF THE PRESIDENT. 



67 



mineral, any more than in the vegetable or the animal kingdoms. 

 All the sciences of nature must be content to recognize individuals 

 as the only real entities, and to accept species, like genera, families, 

 and orders, as convenient but purely artificial conceptions. 



The geological study of minerals leads us to regard each specimen 

 that we examine as possessing a distinguishing combination of 

 properties, some of which are impressed upon it by causes operating 

 when it came into being, while others are no less clearly the result 

 of the long series of vicissitudes through which it has since passed. 



Of all the branches of Mineral Morphology there is none from 

 the study of which the geologist has gained more in the past, or 

 from which he has greater reason to look for future aid, than that 

 of the Embryology of crystals. 



In the year 1840 Link showed that the first step in the formation 



crystals in a solution consists in the separation of minute spherules 

 of supersaturated liquid in the mass ; and subsequently Harting in 

 Holland, and Eainey and Ord in this country, obtained a number 

 of interesting experimental results, by allowing crystallization to 

 take place slowly in mixtures of crystalloids and colloids. 



Valuable contributions to the same subject were made by Frank- 

 heim, Leydolt, and others ; but it is to Hermann Vogelsang that we 

 owe the greatest and most important contributions to Mineral 

 Embryology. By the ingenious device of adding viscous substances 

 to solutions in which crystallization was going on, he succeeded in 

 so far retarding the rate at which the operation took place, as to be 

 able to study its several stages. He thus showed how the minute 

 " globulites 9 gathering themselves into nebulous masses, or ranging 

 themselves according to mathematical laws, gradually build up 

 skeleton-crystals, by the clothing of which the perfect structures 

 arise. 



Since the early and regretted death of Vogelsang, the subject of 

 the development of crystals from their embryos, the so-called crys- 

 tallites, has been successfully prosecuted by Behrens, Otto Lehmann, 

 Wichmann. and other investigators. 



Xow in all glasses — whether of natural or artificial origin — in 

 which the process of primary devitrification is going on, we have 

 examples of the growth of crystals in a viscous and retarding mass, 

 and in these, as Leydolt, Zirkel, and Vogelsang clearly saw, admir- 

 able opportunities are afforded to us for studying the formation of 

 crystallites, and the laws which govern the union and growth of 

 these into crystals. Two years ago, my predecessor in this Chair 



