TRANSACTIONS OF THE SECTIONS, 9 
On a Change produced by Exposure to the Beams of the Sun in the Proper- 
ties of an Elementary Substance. By Professor Draper of New York, 
Communicated by Dr. Kane. 
Dr. Kane preliminarily described the general properties of the solar beam as acting 
on chemical substances, and pointed out the brilliant success with which the experi- 
ments of Daguerre and Niepce, of Herschel, Talbot and Hunt, had been crowned. 
He reminded the Section, that in analysing the solar beam, all parts of it were not 
found equally active in producing chemical effects ; and that, in fact, the conclusion 
was now very generally admitted, that in the solar beam there are three distinct sets of 
rays :—those possessing heating properties, which are the calorific rays; those pro- 
ducing the sensation of light—the luminous rays; and those which effect chemical 
changes, which Dr. Draper proposes to call the Tithonic rays; for he, adopting the 
idea of peculiar matters of light and heat, considers that the chemical effects are pro- 
duced by a peculiar material agent, which he terms Tithonicity. Dr. Kane then pro- 
ceeded to read Professor Draper’s paper itself, which commenced with announcing the 
principle that “chlorine gas, which has been exposed to the daylight or to sunshine, 
possesses qualities which are not possessed by chlorine made and kept in the dark. 
It acquires from that exposure the property of speedily uniting with hydrogen gas. 
This new property of the chlorine arises from its having absorbed tithonic rays, corre- 
sponding in refrangibility to the indigo.” The property thus acquired is not transient, 
like heat, but permanent. A certain portion of the tithonic rays is absorbed, and 
becomes latent, before any visible effects ensue. Light, in producing a chemical 
effect, undergoes a change as well as the substance on which it acts: it becomes de- 
tithonized. The chemical force of the indigo ray is to that of the red as 66°6 to 1. 
The author remarked, that we are still imperfectly acquainted with the constitution of 
elementary bodies, inasmuch as we know, in general, only those properties which they 
possess after having been subjected to the influence of light. 
On Elliptic Polarization in Light reflected from various substances. 
By the Rev. Professor PowELt. 
In a communication to the Association at the Manchester Meeting, the author 
stated, amongst other results connected with this subject, that he had observed the 
phenomena of elliptic polarization in polarized light reflected from several mineral 
substances, in which it had not been (as far as he was aware) hitherto noticed. This 
inquiry bears upon the general question, to what substances is the property of con- 
verting plane into elliptic vibrations in the reflected light, confined? As far as obser- 
vation has yet gone, it seems restricted in general to metallic substances, whether pure 
or compound ; but to this there seem some exceptions, and it remains to be determined 
what proportion of metal in a compound is necessary to produce the result. As these 
questions will require an extensive range of observation for even a limited solution, 
the author is anxious to lay before the Association a list of all the substances he has 
_ examined, in the hope that others will be added to their number, whether by the in- 
dependent experiments of those who may have access to such specimens, or by 
their favouring the author with the loan of such substances for examination. 
The mode of examination is precisely that of which the author gave a sketch at 
the last meeting, and a full account of whish is published in the Philosophical Trans- 
actions for the present year. It is necessary that the specimens for examination should 
present a tolerably plane surface, capable of reflecting a sufficient quantity of light, 
of more than one-tenth of an inch square. 
The foliowing list contains the name of each substance examined, as labeled, and 
in some instances numbered, in the Buckland Collection at Oxford. Those marked 
with (B.) are among the substances examined by Sir D. Brewster. (Phil. Trans. 1830.) 
The proportion of metal given by analysis is added wherever the author has been 
able to find it given. 
