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W. LeConte Stevens—Physiological Optics. 353 
5. Tue Operation oF THE WILL IN VIsIon. 
In reference to the operation of the will upon the muscles of 
the eyes, Helmholtz states that we are limited to efforts for the 
attainment of single and distinct vision. The French edition 
of his great work on Physiological Optics received the last 
corrections of the author, and from this the following quota- 
tions must be made: 
“Tl faut remarquer en général que, dans toutes les mouve- 
ments volontaires, notre volonté ne tend jamais qu’a atteindre 
un résultat extérieur nettement déterminé et perceptible par 
lui-méme.”—Opt. Phys., p. 613. 
“Il résulte de ces faits que la relation qui existe entre les 
mouvements des deux yeux n’est pas commandée par un 
mécanisme anatomique, mais qu’elle se modifie, au contraire, 
sous l'influence de notre volonté; la seule limite réside dans 
le fonctionnement de notre volonté que nous ne savons pas 
appliquer & un but autre que celui de voir les objects simples 
et nettement.”— Opt. Phys., p. 617. : 
The experiments just described show that the will may be 
directed to the attainment of other ends than single and dis- 
tinct vision. Although not affected with any oe or 
other weakness of the muscles of the eyes, and 
6. Bryocunar Viston AND Brnaurat AUDITION, 
The discoveries in reference to binaural audition, made during 
the last few years independently by Professor Silvanus Thomp - 
son,* of England, and Professor A. M. Mayer, of this country, are 
Interesting, not only as additions to our knowledge of physio- 
logical acoustics, but also in relation to the phenomena of 
* Philosophical Magazine, Oct., 1877, Nov., 1878, and Noy, 1881. 
