500 A Study of Growing Crystals by Photomicrography. 



very intense light. Whether or not we shall be able to 

 obtain more positive knowledge with the present apparatus, 

 is a questionable matter. In the near future the attempt 

 will be made here to carry further the work herein described; 

 but it is doubtful if any more definite results will be obtained. 

 The great speed of initial growth casts a measure of doubt 

 over some of the observations of Link and his followers. 

 Is is not possible that the subjective effect of the rapidly 

 growing crystal might be mistaken for that of a globule of 

 liquid ? Even upon the photographic plate there is a slight 

 resemblance, and in one or two cases deliberate study is 

 needed to detect evidence of structure in the smallest crystals. 

 In conclusion, the report of the foregoing pages may be 

 summarized as follows : — It has been found possible to take 

 very frequent photomicrographs of crystals during their birth 

 and growth. An enlargement of over four thousand dia- 

 meters was obtained, and both common and polarized light 

 were used. Only substances with high melting-points were 

 examined, and the crystallization was always from aqueous 

 solution. No properly focussed image on any of the plates 

 seemed to be devoid of crystalline structure. The growth in 

 diameter during the first second of the crystal's life was found 

 to be vastly greater than during the subsequent period. Not 

 the diameter itself, but a power of the diameter, was pro- 

 portional to the time under the conditions used in our 

 experiments. This exceedingly rapid initial diametric growth 

 accounts for a lack of definition noticed in the first images, — 

 a lack of definition sufficient to have misled the eye, but not 

 enough wholly to obscure the photographic evidence of 

 crystalline structure. 



Hence we may conclude that whatever theoretical reason 

 there may be for believing that crystals always develop from 

 a transitory liquid phase, the present experimental evidence 

 is inadequate to prove that these globules attain a size visible 

 in the microscope, except in the case of substances which 

 melt at temperatures not far from the temperature of crys- 

 tallization. The present paper is to be regarded rather as 

 the suggestion of a mode of study than as a finished treat- 

 ment of the subject, however. 



The apparatus might be used to obtain a series of kineto- 

 scopic pictures of insects or other small animals or plants y 

 and is now being used for the study of the change in structure 

 of steel at high temperatures. We are indebted to the 

 Rumj'ord Fund of the American Academy of Arts and 

 Sciences for some of our apparatus. 

 Cambridge, Mass., October 1898 to October 1900. 



