6 REPORT—1845. 
On the Heat of the Solar Spots. 
By Professor Henry, of Princeton College, New Jersey. 
Sir D. Brewster read an extract of a letter which he had just received from Prof. 
Henry, who had recently been engaged in a series of experiments on the heat of the 
sun, as observed by means of a thermo-electrical apparatus applied to an image of 
the luminary thrown on a screen from a telescope in a dark room. He found that 
the solar spots were perceptibly colder than the surrounding light surface. Prof. 
Henry also converted the same apparatus into a telescope, by placing the thermo- 
pile instead of the eye-glass of a reflecting telescope. The heat of the smallest 
cloud on the verge of the horizon was instantaneously perceptible, and that of a 
breeze four or five miles off could also be readily perceived. 
Description of a Universal Stand applicable to the Use of Astronomical Tele- 
scopes. By M. Bocusuawski. Communicated by the Rev. Prof. Cuaxus. 
A solid cylindrical axis, which in its normal position is vertical, carries at its 
upper extremity the two supports of a horizontal axis, at one extremity of which is a 
graduated circle A, and at the other, the telescope haying its direction of collimation 
perpendicular to this axis. The solid cylinder turns in a hollow cylinder of double 
the length of the telescope, and having at its upper end another graduated circle B. 
The hollow cylinder rests at about its middle on two supports, which stand on a 
circular base adjustible by foot screws. It is also capable of motion about a hori- 
zontal axis, and carries at its lower end a counterpoise to the weight of the telescope 
and circles, and a graduated arc, by means of which its axis may be set to any re- 
quired elevation. The instrument may consequently be either a portable transit, or 
a transit-circle, or an altitude and azimuth instrument, A being the altitude and B 
the azimuth circle, or, lastly, an equatorial, in which case A is the declination circle 
and B the hour circle. The telescope is in no case in a position in which observa- 
tion is impracticable. ee, Se 
On certain Points in the Elliptic Polarization of Light by Metallic Reflexion. 
By the Rev. Professor Powstt, M.A., F.R.S. 
The object of this communication was supplementary to one given last year (see 
Sectional Proceedings, 1844), since which time the author has continued his re- 
searches into some parts of the subject not before adverted to. 
The original plane of polarization being inclined 45° to that of incidence on the 
metal, in the lower degrees of ellipticity, i. e. at lesser incidences, the dislocated 
rings preserve the distinction of the dark and bright systems ; which they lose when 
the vibrations are absolutely circular: also at the position of the analyser interme- 
diate to the rectangular positions, the coloured arcs assumed a peculiar distorted 
appearance. 
A generalization of the formula, employed in the author’s paper, Phil. Trans. 
1843, so as to include all positions of the polarizer and analyser, and assuming the 
component vibrations with general or unequal coefficients, is necessary for explain- 
ng the last-mentioned phenomenon; while the former supplies the best means of 
directly observing the change in the virtual plane of polarization of the reflected ray, 
by means of the position necessary to be given to the analyser to restore the same 
system of rings: as e. g. that for dark branches. 
These changes in general are analogous to, but not the same as, those in the re- 
flexion from transparent bodies examined by Fresnel. But at the incidence for the 
maximum, as well as at that nearest the perpendicular, they are the same. 
At small incidences, in his former communication*, the author mentioned that he 
had been led to suppose an anomaly in this respect, the arc appearing to deviate 
from 45°. But more recent and careful repetitions have shown that the results are 
really conformable to the law in this case. 
He has carried on a considerable series of observations of the change of plane at 
different incidences, and for various metals, &c. In regard to the maximum ellipti- 
* See British Association Report, 1844, Sectional Proceedings, p. 7. 
