AMOS PEASLEE BROWN. xih 



to correlate the variations which they exhibited with differences of 

 environment, and to show the effect of isolation in their evolution. 

 To illustrate graphically the extent of their variation he devised 

 some ingenious plottings and curves, based upon actual measurements 

 of each individual shell, for by adopting measurements as his basis 

 of comparison he hoped to eliminate as far as possible the personal 

 equation. This whole investigation illustrated the constant trend 

 of his mind toward mathematical methods. Another paper along 

 very similar lines dealt with variation in two species of Lucidella.~* 

 Still another Jamaican study was responsible for a paper on the 

 method of locomotion in certain land snails-^ — a distinctly original 

 piece of work. He had found that certain species possessed a com- 

 paratively very rapid rate of progression and a careful study dem- 

 onstrated that they had an entirely different method of locomotion 

 from that of the majority of snails. The foot, he found, touched 

 the surface upon which they walked only along its edges, while the 

 wave motions which traversed it were in the opposite direction to 

 that usually prevailing in these mollusks. Furthermore the shell 

 was carefully balanced on the operculum and swayed from side to 

 side as the animal advanced. The rapidity of the wave mo'tions 

 and the exact rate of progress were worked out in much detail. 



During the period just described two mineralogical publications 

 were issued in which Brown's name appears as joint author. One 

 of these, in the preparation of which he was associated with Dr. 

 Persifor Frazer, consisted of a series of tables for the determina- 

 tion of minerals by physical properties,^® while the other in which 

 Dr. Frederick Ehrenfelt was his associate was a report on the min- 

 erals of Pennsylvania-^ published by the Topographical and Geo- 

 logical Survey of the State in 1913. 



In the summer of 191 3 Brown made another trip to the tropics, 

 touching at Georgetown, British Guiana, and spending some time 



2* " Variation in Two Species of Lucidclla from Jamaica," ibid., 1913, 

 pp. 3-21. 



25 " The Method of Progression of Some Land Operculates from Ja- 

 maica," The Nautilus, XXIV., No. 8, December, 1910, pp. 85-90. 



26 " Tables for the Determination of Minerals by Physical Properties," 

 Philadelphia, J. B. Lippincott & Co., 1910, pp. i-xiii, I., 1-125. 



27 " Minerals of Pennsylvania," Topog. and Geolog. Survey of Penna.. 

 Report No. 9, pp. 1-160, 1913. 



