OfiLighi. 417 



least refrangible rays, and at last became black, but was not 

 affected in the most refrangible rays. The same change was 

 produced by exposing it to a current of hydrogen gas. The oxide 

 of mercury from calomel and water of potash, when exposed to 

 the spectrum, was not changed in the most refrangible rays, but 

 became red in the least refrangible ; which must have been owing 

 to the absorption of oxygen. The violet rays produced upon 

 moistened red oxide of mercury, the same effect as hydrogen gas. 



Dr. Wollaston found, that guaiac, exposed to the violet rays, 

 passed rapidly from yellow to green; and MM. Gay Lussac and 

 Thenard applied to the same influence a gaseous mixture of hy- 

 drogen and chlorine; when explosion immediately took place. 

 By placing small bits of card, coated with moist horn-silver, or 

 little phials of those mixed gases, in the different parts of the 

 spectrum, M. Berard verified the former observations of the che- 

 mical power acquiring a maximum in the violet ray, and existing 

 even beyond it ; but he also found, that by leaving the tests a 

 sufficient time in the indigo and blue rays, a perceptible effect 

 was produced upon them. He concentrated by a lens all that 

 portion of the spectrum which extends from the green to the ex- 

 treme boundary of the violet ; and by another lens he collected 

 the other half of the spectrum, comprehending the red. The 

 latter formed the focus of a white light, so brilliant, that the eye 

 could not endure it ; yet in two hours it produced no sensible 

 change on muriate of silver. On the contrary, the focus of the 

 other half of the spectrum, whose light and heat were far less in- 

 tense, blackened the muriate in ten minutes. The investigations 

 of Delaroche enable us, in some measure, to reduce these dis- 

 similar effects of light to a common principle. See Caloric. 



In Mr. Brande's late Bakerian lecture on the composition and 

 analysis of coal and oil gases, this ingenious chemist shows, that 

 the light produced by these, or by olefiant gas, even when con- 

 centrated so as to produce a sensible degree of heat, occasioned 

 no change on the colour of muriate of silver, nor on a mixture 

 of chlorine and hydrogen ; while the light emitted by electrized 

 charcoal, speedily affects the muriate, causes these gases to unite 

 rapidly, and sometimes with explosion. The concentrated light 

 of the moon, like that of the gases, produced no change. He 

 concludes with stating, that he found the photometer of Mr. 

 Leslie ineffectual. He employed one filled with the vapour of 

 ether (renewable from a column of that fluid), which he found to 

 be more delicate. 



The general facts, says Sir H. Davy, of the refraction and ef- 

 fects of the solar beam, offer an analogy to the agencies of elec- 

 tricity. In the voltaic circuit, the maximum of heat seems to be 

 at the positive pole, where the power of combining with oxygen 



Vol. 57. No. 278. June 1821. 3 G 



