illiam Rowan Hamilton. 297 
In 1828 Hamilton became a Fellow of the Royal Astronom- 
“ical Society, and thus at the time of his decease was among the 
oldest, as his name was certainly among the most honored, of 
our members. In 1833 he made known, in one of several sup- 
plements to the “Theory of Systems of Rays,” his great discov- 
ery of Conical Refraction. In this memoir, starting again from 
the principle of least action, and, as before, conducting the inves- 
tigation by means of a single Principal Function, he establishes 
the entire theory of double refraction; and, applying it to the 
case of biaxial crystals, by a new and simpler method’ than that 
originally pursued by Fresnel, he obtains the equation to the 
form of the wave assumed by the vibrating ether within the 
erystal. On examining the form of the wave surface, Hamilton, 
with remarkable sagacity, observed that if the theory and the 
results were true, a single ray of light incident at a certain angle 
on a biaxial crystal, must of necessity pass into it, not as one ray, 
nor even as two rays, but as a conical sheet of light, and then 
finally emerge as a luminous cylindrical surface. And, again, 
his profound and complicated analysis indicated that there was 
also a direction within the crystal, such, that if an internal ray 
of light passed along it, it would emerge from the crystal, not as 
one ray, but as a luminous conical shell. Such results as these 
were not only apparently contrary to all analogy one expecta- 
experiment was at length successfully performed by Dr. Hum- 
phrey Lloyd, of Dublin, whose patient ingenuity, and faith in 
in a crystal, into an infinite number of rays, forming the surface 
of a luminous cone. 
process by a very elegant 
._| It is but a point of justice to state that Mr. Archibald Smith has since much 
ed icit method of elimination. _ 
‘proved the simplicity of the 
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