POLARIZATION BY REFLECTION. 
71 
best memoir giving the mathematical theory of double refrac- 
tion in various crystals, demonstrated by experiment. This 
prize was awarded in 1810, to M. Malus, Lieutenant Colonel 
in the Imperial Guards, and member of the Egyptian Institute. 
In 1808, while Malus was engaged in his experiments on 
double refraction, and was casually observing through a double 
refracting prism the light of the setting sun as it came reflected 
at a certain angle from the windows of the Luxembourg 
Palace, in Paris, on slowly revolving the prism between his 
eye and the light, he was surprised to see a remarkable differ- 
ence in the brilliancy of the two images, the most refracted 
gradually changing from brightness to obscurity, and the re- 
verse at each quadrant of revolution. A phenomenon so un- 
expected led him to investigate its cause, and in the progress of 
his inquiries he discovered that every substance in nature, 
having a polished surface, is capable of polarizing light by re- 
flection at a specific angle peculiar to each substance. The 
impetus thus given to scientific curiosity, attracted to the study 
of polarized light a constellation of talent almost unrivaled at 
any period in the history of science. So extensive have been 
the investigations, and so wonderful the phenomena discovered, 
that the subject of polarized light now justly ranks as one of 
the most elegant and refined branches of physical optics. 
The phenomena of polarized light will here be described 
only so far as to enable the reader to understand their applica- 
tion to investigations connected with the microscope. Brews- 
ter’s Optics, Pereira’s Lectures, and other elaborate treatises in 
common use, will furnish fuller details to those who desire to 
pursue the subject. 
96. Polarization toy reflection. When a ray of light is 
reflected from a plate of glass, or the polished surface of any 
other substance, it can usually be reflected again from another 
similar surface, and it will pass freely through transparent 
bodies. If, however, a ray of light be reflected from a plate of 
glass, at an angle of 56° 45', it becomes incapable of reflection 
at the surface of another plate of glass in certain definite posi- 
tions, but it will be completely reflected by the second plate in 
CATALOGUE OF ACHROMATIC MICROSCOPES. 
