JOURNAL 
OF THE 
WASHINGTON ACADEMY OF SCIENCES 
Vou. 13 Marcu 4, 1923 No. 5 
PHYSICS.—The measurement of light.) E. C. Crirrenpen, U. S. 
Bureau of Standards. 
INTRODUCTION 
I believe that custom allows the annual address of your retiring 
president to differ from other papers presented before the Society in 
at least one important respect. Others are expected to bring before 
you something original in theory, mathematical development, or 
experimental data. Your president, however, is permitted to choose 
his own subject without having to convince the Committee on Com- 
munications that it will involve an addition to our knowledge of 
physical science. Taking advantage of this liberty, I have chosen to 
talk on the subject of the measurement of light, with the intention 
of discussing problems which will be quite familiar to many of you, 
and of summarizing established facts rather than attempting to set 
forth any new ones. My reasons for so doing are two-fold. First, 
there has recently arisen in the scientific and technical press an unu- 
sual amount of discussion of this general subject; and second, some 
of the published discussions, as well as questions which have come 
up otherwise, have indicated that there is a certain degree of haziness 
in our general ideas on the subject. 
It is perhaps well to recall also that during the year just past the 
Society has been favored with two important papers rather closely 
related to this subject. Dr. Troland in January gave us a carefully 
reasoned discussion of general principles applying to the study of 
problems of sensation, which involve physiological and psychological 
processes as well as physical stimuli. More recently Dr. Gibson has 
presented the results of his thorough-going experimental determina- 
1 Address of retiring President, Philosophical Society of Washington, January 13, 
1923. The text has been modified as made necessary by omission of slides and other 
illustrative material used in its presentation. 
69 
