32 
REPORT—1847. 
distinguish it from the aoalogous influence of quartz, which is m^ested oa^is 
the direction of the optic axis. 
Since the preceding remarks were put together. Dr. Apjohn has found that tte 
of light polarized by reflexion, and made to disappear by the interpositioD rf a 
choli's prism, was restored when traiasmitted thruugli a particle ofhjilftfai 
Fraokfort'OD.tbc.Maine. All varieties therefore of this mineral may be wddei 
to possess the same optical pro|>ertics. 
'1*0 this notice Dr. Apjohn wishes to add that, on continorng his eipefii#e‘*i! 
has since found the results to be somewhat diflercot according totkpanufx 
lamina of layalite traversed by the light, the change in the position of flepind 
polarization not having always the same direction or value, and bebg «asia# 
null; a fact which would seem to point to a dificreut explanation of the phauoai 
from that already suggested, and to identify the optical characters of 
those of rock crystal, the differences being explicable upon the hypothe^isoflkh- 
mer ininerul being composed cif a multitude ii( aiiiiute crystals of the latter, fc** 
together without any regular or symmetric arrangemeot. 
On the Poliirizeition of the Atmosphere. 
Ih/ Sir David Brewstek, K.H., D.C.L.,F.R.S.lAmd,ii 
Sir David Brewster read a paper on the Voltxrizaliun of the AtiiuMphfTe,ai<^ 
lubited a Map of the Lines of Equal Polarization, which he had projected fix* 
Bhysirnl Atlas of Dr. Berghaus and Mr. Jolmston. In this paper he treated-" 
1 • Of the neutral point discovered by M. Arago. , 
2. Of a secondary neutral point which he had discovered accompanyiflg 
M. Arago. 
.1. Of the neutral point above the sun discovered by M. Babinet. 
4. Of (he neutral point helow the siin discovered by himself. 
5. Of the maximum polarization of the sky. 
form of the lines of equal polarization ia the atmosphere. 
1 r I ^ c^oDstruction of the map of the lines of equal polarization. 
Under these serwn heads the author gave a brief account of the results of 
^‘rvalions on the polarization of the atmosphere, made during upwards of fou' 
at ht. Andrew s. near the level of the sea. The observations were made with 
nir/er of his own invention, by which he measureil the polarization of ^y 
* fonipensating and opposite polarization indicated by the polarimeKf- ^ , 
way he ascertained that the curves of equal polarization have the general cb»rK 
cmnis^tes, resembling the curves of equal double refraction in Inaxal . 
biaial crysua '' '‘h the poles of no polarization, or the optic no 
In the normal stale nf the atmosphere, at sunrise and sunset, the 
u ral jwint from the sun, or from the point op|>osite the son, is taken ^ 
As the su!, descends below the horizon. 
IKunt separates from the antisolar point, or the point opposite W 
As the sun rises the other two neutral pointskpproach to his disc, 
the meridian they separate from it. When the sun is in the the 
of curves » the same as that of uniaxal crystals. 
On a A>w Species of Polarization related to the direction of the J 
ar.H,rcl Suifaces. By Sir David Brewster, 
Und. .y V.P.H.S. Bdin, 
stJl ‘" l-"'» described in this notice were observed in specimens 
t ‘^y late Sir John Barton. Tbe^^ 
larec n„rr' the transverse bands exhibited by certain grooved surfaces, ^ 
aur^c^a ^ surface is remov^ or cut awav by the 
•Vrb.d\Lmr'' particularly referred to in the author's paper 'Ou a Nc^ 
Bodies ' dum; i f by the Grooved Surfaces of MetalUc 
* published in the Philosophical Transactions for 1829, P- 301-316- 
