696 TRAVEL IN EUROPE AND AMERICA. [1880, 
come 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 Ae ‘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 Ill sit down and study your Pinus 
paper, which I have not looked at yet, so absorbed 
have I been. . . . 
