164 . Proceedings of the British Association. 



capable of combustion which could be had ; and in order to have 

 a suitable combination, he used an oxygen light analogous to the 

 Bude light. Every one conducting these experiments was aware 

 that it was necessary to pass the light through a narrow aperture ; 

 but this would reduce the intensity of the light so much, as to 

 make it difficult to observe the rays at the extremity of the spec- 

 trum ; but he found that he could obtain the effect of a small 

 aperture by merely inclining the prism ; so that with a good 

 prism, the great lines in the solar spectrum might be seen by 

 using an aperture three or four feet wide, the whole breadth of 

 the window, by the mere inclination of the prism, which had 

 the effect of producing a narrowing, facing the light. He had 

 obtained two hundred or three hundred results which he had not 

 had any leisure to group; but he would mention some of the gen- 

 eral results. When nitrate of lead was thrown into combustion, 

 remarkably fine lines were produced in the spectrum. The lu- 

 minous line D of Fraunhofer, existed in almost every substance, 

 especially in all into which soda entered, particularly in the flame 

 of a common tallow candle: probably owing to the muriate of 

 soda existing in the tallow. The hydrate of strontia and the 

 iodide of mercury gave the lines very remarkably in yellow and 

 green. Also in that remarkable substance, the lithoxanthemate 

 of ammonia, first discovered and published by Mr. Fox Talbot, 

 the fine lines were seen throughout the whole length of the spec- 

 trum; and there was a remarkable blue band, which he (Sir D.) 

 had not distinctly recognized in any other flame. Indigo gave 

 fine green and orange lines at equal distances from the D of 

 Fraunhofer. Prussian blue did the same : calomel, nitrate of 

 magnesia, litharge, also showed lines; the sulphocyanite of pot- 

 ash gave a violet and orange flame, with the lines extremely dis- 

 tinct. He hoped at the next years meeting of the Association 

 to be able to embody these various results in a regular report. 



Sir D. Brewster made a communication on a New Property of 

 the rays of the Spectrum, with observations on the explanation 

 of it given by the Astronomer Royal, on the principles of the 

 Undulatory Theory. If we cover half the pupil of the eye 

 with a thin plate of any transparent body, and thus view a pris- 

 matic spectrum, so that the rays which pass by the plate inter- 

 fere with those that pass through it, the spectrum is seen crossed 

 with beautiful black and nearly equidistant bands, whose breadth, 

 generally speaking, increased with the thinness of the plate. If 



