112 Scientific Intelligence. 
have been shut off by a thin disc oe with its edge towards si eye, 
ce 
of the disc), I have often been a le to mark the opposite polarinations 
and the Spaeee of the neutral points with perfect ease, even at mic 
n our climate it is by no means unusual to have days on which 
al! the three neutral points can be observed, and their places determined. 
During the whole period of Brewster’s observations at St. Andrews, he 
found but two such days, April 5th and 8th, 1842, (loc. cit., pp. 124, 
7.) Quasi-neutral lines, — bands of opposite  aeieeea can - 
found in crete . parts of the sky by rotating the polari 
the line of maximum positive or negative paladin “But aia 
additional ‘elisicsl will show that the neutralization is only apparent. 
The position of a true neutral point can be determined by swee ing 
its neighborhood alternately with the vertical and with the horizontal 
polarized bands forms curves with a ny wae 4 determined by the position 
of the sun or of the anti-solar point 
(10.) Some of my observations have indicated an apparent os 
between these curves and the magnetic dip and terrestrial latitude. I 
have not been able to satisfy myself w whether the co octet was 
merely ee or whether it indicated another point of analogy be- 
ey the laws of light and of magnetism. 
“a8 varying effects of haze and cloud, appear, on the whole, to 
‘aes Brewster’s theory, that the neutral point is produced ‘by the op- 
posite action of light polarized by reflexion and refraction.” ged pp: 
123, 169, 176, 178, 180. 
In one oe soon after sunset, the reflection from aihiaceed 
clouds i in the neighbor me: the anti “solar r point was such as to totally 
oO 
ot Points ;* by Putny Ears Cuassz, 2 A., 8.P.A.S.—In my eommuni- 
cation of Janudr 2 ies, I stated that when Brewster's neutral point is 
above the. horizon, I had frequently determined its position with great 
* Tam not sure whether this is the “singular effect” thus described by aphdlag a 
(loc. cit., p. 124); ress soorsying the Shiga vertically round, the neutral sain 
ond ging fou har igi a » Was the arc of a circle, to whi 
the bands was a (See, also, , PP. 121, 167.) 
? From the Prasstioes of the American Philosop hical Society, April 6, 1866. 
