262 Scientific Intelligence. 
which had been passed through aqueous hydrochloric acid. Sending 
the polarized ae through the tube, I placed myself in front of it, 
my eye g on a level with its axis, my assistant, Mr. Cottre il, 
occupying a enitet Fes behind the tube. The short rt diagonal 
the light continued to act, a superb blue cloud visible to both my 
assistant and myself — slowly £0 formed. But this cloud, so deep 
and rich when looked at from the positions mentione , utter y dis- 
perenne when looked a uowteaidy downward, or ver tically up- 
ward. Reflection from the cloud was not possible i in these direc- 
ions. When the large Nicol was slowly turned round its axis, 
when looked at downward or upward. This truly fine experi- 
ment was first ripe Pic ita by a ‘remark addressed to me 
in a — es Prof. Sto 
Now gards the Felaiaion of skylight, the greatest stum- 
raed ‘blog | hes hitherto been that mentee with the law of 
er, operated upon aber ntes of widely different refractive indices, 
and therefore of very different polarizing angles as ordinarily de- 
fined, but the pularinatiog! of the beam by the incipient cloud has 
thus far proved itself to be absolutely ia of the polari- 
zing angle. The law of Brewster does not apply to matter in this 
condition, and it rests with the undu are theory to explain why. 
Whenever the some Sarees particles are sufficiently fine, no matter 
what the substance forming the particles may be, the direction of 
maximum polarization is = right angles to the illuminating beam, 
the polarizing angle for matter in this condition bein riably 
45°. This I consider to be a —_ of capital stipdrtunbe with ref 
: ey ai be obtained in this exceeding- 
i fine state of division, no produce the same effects, does not 
admit of reasonable doubt. And that they must exist in this con- 
* The difficulty referred to above is thus expressed by Sir 1, Herschel :— 
The cause of the polarization is evidently a reflection of the s pe 
w a a) 
a single reflection, 
refraction, which is the tangent of that angle: other wo! 
then woullt require to be mse és wir apesate?*< ascaclone "par. 233). 
a ee ee Se 
