696 TRA VEL IN EUROPE AND AMERICA. [1880, 



coine Monday and take it, I will lend it to you for 

 that week. 



Professor Fisher has sent me an admirable sermon 

 on " The Folly of Atheism." Have you seen it ? 



... I would change a word in paragraph seven. 

 If by proof you mean demonstration of its truth, I 

 remark that rational explanation of the phenomena, so 

 far as known, does not prove an hypothesis. Two 

 different hypotheses may do that ; and it may long be 

 impossible to get a* crucial test. 



Sincerely yours, A. GRAY. 



Dr. Gray was at work on another part of the " Syn- 

 optical Flora." Asters had always been his especial 

 study, and a great and puzzling labor, and these few 

 lines tell of his difficulties. 



TO GEORGE ENGELMANN. 



April 17, 1880. 



We heard only incidentally of your accident, and 

 were very sorry. Do be careful. Don't climb lad- 

 ders. Leave that to young fellows like me ! ... 



I am half dead with Aster. I got on very fairly 

 till I got into the thick of the genus, among what I 

 called Dumosi and Salicifolia. Here I work and 

 work, but make no headway at all. I can't tell what 

 are species and how to define any of them, nor what 

 the nomenclature is, i. e., what are original names. 



I will take this group abroad, but it will be just as 

 bad there, unless I can get some settled ideas before 

 I start. I never was so boggled. 



To-morrow I '11 sit down and study your Pinus 

 paper, which I have not looked at yet, so absorbed 

 have I been. 



