292 
GILBERT. 
Acknowledgments .—Before my final bow is made it is due 
that a moment be given to recognition of the facilities and 
aid I have received in the conduct of the investigation. 
Through the courtesy of Captain McNair, superintendent of 
the Naval Observatory, and with the cordial cooperation of 
the astronomers of his staff, I have been enabled to study 
the lineaments of the moon’s face through the great Wash¬ 
ington equatorial. The kindness of Professor Rood and 
Professor Hallock accorded me ample space and facilities 
for experimentation in the Physical Laboratory of Columbia 
College. The courtesy of Professor Langley, Secretary of 
the Smithsonian Institution, and the generosity of Professor 
Hale, of Chicago, secured for my study fine series of lunar 
negatives and photographs. 
The progress of my work has carried me in many direc¬ 
tions beyond my proper field of physiography into the fields 
of physics and celestial mechanics, and in these unfamiliar 
ways my hesitating feet have been guarded and guided by 
certain masters in those fields whom I am no less fortunate 
than proud to number among my friends. I refer to Pro¬ 
fessor Newton, of Yale College, and to our fellow-members, 
Dr. Bar us, Professor Abbe, and Professor Woodward. 
