MR. POWER ON THE ABSORPTION OF THE SOLAR RAYS, ETC. 
37 
it is sometimes called, will be right-handed or left-handed according as a is positive 
or negative. In the latter case we may put the formula under the shape 
cot y= cot C.a'S, 
or 
which shows that for a negative value of a of equal magnitude, the left-handed spiral 
will be exactly similar to the. right-handed spiral. 
Since the nature of the spiral as regards right and left depends on the sign of s — s ' ; 
when this difference is very small, as it must be when there is no sensible reflected 
ray (this appears by the value of q'), we see how a very trifling variation of the con- 
stitution of the fluid will change the rotation from right to left or from left to right; 
and this is agreeable to experience; for though the chemist can detect no difference 
in sugar formed from beetroot and that formed from the cane, yet these are found to 
possess the property in opposite directions. In the same way the specimens of right- 
handed and left-handed quartz which possess this property, must owe their difference 
to the presence of some ingredient, which enters in so minute a proportion as not 
sensibly to affect either the crystalline form or the chemical composition. 
I must say that this successful application of the present theory to the explanation 
of these singular phenomena, which no one, so far as I am aware, has ever attempted 
to explain before, gives me great confidence in the truth of the general theory; nor 
less satisfactory is the perfectly simple and easy manner in which the known laws of 
refraction, polarization and photometry result from the calculus. I think I may also 
appeal to the symmetry and elegance of the formulae themselves, as justifying the 
inference that they are not less connected with truth than with light. 
37. Several other modes of testing the truth of the present theory have occurred to 
me, but I have not the time to work them out in detail. Suffice it to say, that hitherto 
I have not met with a single case with which it seems to be at variance, and I doubt 
not, whenever the theory of resonance is brought to perfection, that much which is still 
obscure will be completely explained. The latter theory is at present in a very im- 
perfect state, though the experimental researches of Savart and others have revealed its 
phenomena with great minuteness of detail, and with a variety of most curious and 
interesting results. The mathematical difficulties of the subject are such that they 
will require the highest analytical powers to contend with them ; though I cannot 
hope personally to assist in overcoming them, I am very sanguine that they will 
finally yield to the intellectual battery of modern analysis, and I am not a little 
encouraged in this hope by the appearance of M. Lames admirable work, ‘ Lemons sur 
la Theorie Mathematique de l’Elasticite des Corps Solides,’ 8vo. Paris, 1852. Having 
mentioned the name of M. Lame, I beg to call attention to the circumstance that his 
results, as regards the direction of vibration in the polarized ray, coincide with what 
I have obtained in the present theory, being opposed to those of Fresnel and the 
more recent researches of M. Cauchy. See “ Legons,” &c., p. 132. 
