THE PROGRESS OF ASTRONOMY IN 1900. 149 
This is considerably smaller than the recent determina¬ 
tions by Doolittle and A. Hall, Jr., which gave about 20".55. 
The larger value is undoubtedly indicated by recent investi¬ 
gations, but it is not yet possible to fix the figure with confi¬ 
dence. Some defect still inheres in the theory of aberration 
or in the method of its determination, and nothing but long 
continued and persistent effort will solve the mystery. 
