THE 
AMERICAN JOURNAL OF SCIENCE 
[THIRD SERIES.] 
+O 
Art. XXIX.— Recent Progress in Optics ;* by W. LECONTE 
STEVENS. 
Introductory. 
THE reviewer who aspires to give an account of recent 
progress in any department of science is met at the outset by 
two causes for embarrassment: What beginning shall be 
selected for developments called recent? What developments 
shall be selected for discussion from the mass of investigations 
to which his attention has been called? So rapidly is the 
army of workers increasing, and so numerous are the journals 
in which their work is recorded, that the effort to keep up with 
even half of them is hopeless; or, to borrow a simile employed 
by the late Professor Huxley, “‘ We are in the case of Tarpeia, 
who opened the gates of the Roman citadel to the Sabines, 
and was crushed under the weight of the reward bestowed 
upon her.” 
I have selected a single branch of physics, but one which 
can scarcely be treated rigorously as single. From the physical 
standpoint optics includes those phenomena which are pre- 
sented by ether vibrations within such narrow limits of wave 
length as can affect the sense of sight. But these waves can 
scarcely be studied except in connection with those of shorter 
and of longer period. Whatever may be the instruments 
employed, the last one of the series through which informa- 
tion is carried to the brain is the eye. The physicist may fall 
into error by faulty use of his mathematics; but faulty use of 
the senses is a danger at least equally frequent. Physiological 
* Address delivered by the Vice-President of Section B at the meeting of the 
American Association for the Advancement of Science, August 29. 
Am. Jour. Sci—TuirD Series, Vou. L, No. 298—OcrToBErR, 1895. 
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