516 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
corrections obtained from the formula m cos a-\-n sin a, were introduced 
by observers whose records were made too early. 
Another peculiar form of personal equation arises in the observation of 
very faint stars, such as can be seen only in a dark field and observed 
with bright threads. 
Abnormal personal equations in such cases have been suspected for 
some time, and an investigation, lately undertaken but not yet completed, 
shows that all classes of observers have a personal equation for such stars 
different from their ordinary errors and one that cannot be inferred from 
those obtained from the work on ordinary stars. 
A communication was also presented on Cambrian Rocks in 
Tennessee, by Mr. Cooper Curtice. 
320th Meeting. May 12, 1888. 
President Mallery in the chair. 
Seventy-five members and guests present. 
The President announced the death of H. F. Walling, at 
Cambridge, Massachusetts, on April 8, 1888. 
It was also announced that the meeting of May 24 would be 
the last meeting of the Society before the customary summer 
recess. 
Mr. W. A. Croffut, upon the invitation of the Society, gave a 
series of Experiments in Hypnotism. 
Dr. G. Stanley Hall, who was also present by invitation, 
followed Mr. Croffut with some remarks and experiments upon 
the same subject. 
321st Meeting. May 26, 1888. 
President Mallery in the chair. 
Thirty members and guests present. 
The Chair announced the death, on May 24, of Ezekiel 
Brown Elliott, a founder of the Society, and stated that the 
General Committee desired to refer appropriate action to the 
full meeting of the Society. 
