72 The American Geologist. February, 1892 
remained quiet but a very few days, when he visited Highland 
Park (near Chicago) and Milwaukee, where he gave publie lee- 
tures. Immediately on returning home again he entered on a 
course of four lectures on Lvolution, delivered before the Geolog- 
ical Society of Ann Arbor. His weakness increased, and he 
could with difficulty walk to the lecture hall in the University 
buildings. The fourth lecture was never given, because the 
family physician, summoned against his protest, interposed, and 
before he could be restored death had put his veto upon it. 
The malady with which he had suffered for many years, and 
which he fully understood himself, but never mentioned to his 
family, crept upon him very slowly to its fatal termination. He 
had noted for several months that he became easily wearied 
physically. His breathing was difficult, and he had asthmatic 
symptoms. Nights he slept little, sometimes being compelled to 
rise in order to obtain relief from hard breathing, or panting. 
This he attributed to heart disease, but still kept about his work. 
Finally, when confined to his room, and mostly to his couch, he 
was regretful of the time he was compelled to lose in that way. 
His mind apparently ran over the themes of his lectures, and he 
planned new topics. ‘You must not think Lam idle, though lying 
here,” said he, ‘‘for T have laid out two or three articles to be 
written.” Later, the same day, he said: ‘I believe I can dem- 
onstrate mathematically the necessity of a modification of the 
nebular hypothesis of La Place.” Still later he explained what 
he meant by the modification which should be made in the nebu- 
lar hypothesis. ‘I believe I can show mathematically that each 
successive annulation was accompanied by, and caused, an en- 
largement of the orbits of every earlier ring; and that the various 
orbital diameters of the resultant planets have been enlarged from 
time to time, or pushed away from the residual mass.’’ When it 
was remarked to him that the La Placean hypothesis required a 
constant shrinkage of the central mass, having once been extended 
to the utmost limits of the solar system, and that by loss of ring 
after ring it had been reduced to its present condition and size, 
‘‘Ah well,” said he, ‘‘let those defend that who believe it, I be- 
lieve that, like an exogenous tree-trunk, the outer diameters can 
be shown to have been enlarged from time to time.”” This seems 
to be a new conception. It certainly would have been embraced 
in his ‘‘World Life,”’ had it ever been presented before, but we 
