398 Original Articles. [July, 



discovery of the monochromatic character of a sodium light. In both 

 these spectroscopic and also photographic experiments, the principle 

 of identifying effects by wave lengths was resorted to, a suggestion 

 naturally occurring from the use of the interference spectrum. 



IV. On the Variations of the Light of Flames with the Temperature. 

 — One of the most important facts demonstrated in these memoirs, 

 indeed, it almost rises to the position of a general law, is this — " that 

 the more violent chemical action the more refrangible the emitted light." 

 In the combustion of an elementary solid, such as carbon, if air be 

 more and more vigorously supplied, rays of continually-increasing 

 refrangibility emerge, and if, instead of air, oxygen be used, the result- 

 ing spectrum rivals that of the sun in brightness and extent. On this 

 principle, that increasing vigour of chemical action implies increasing 

 frequency in vibration, Dr. Draper gives an explanation of the colours 

 emitted by flames. Thus carbonic oxide burns with a blue light, 

 because it needs but little oxygen to complete its combustion, but the 

 light of burning cyanogen increases in refrangibility when its com- 

 bustion is made in oxygen gas. Among the most striking of these 

 results, as showing the complete control that the circumstances of a 

 combustion have over the character of a flame, is the extraordinary 

 spectroscopic appearance of the blue blowpipe cone, when contrasted 

 with the flame from which it originates, a singular instance which has 

 been much overlooked. In descriptions of the changes in the spec- 

 trum caused by variations in the rate of combustion, the appearances 

 produced by substances volatilizing in a flame, must not be confounded 

 with those produced by a body that is oxidizing. There is no reason 

 at present to believe that the spectral lines in the former case can be 

 made to alter their position by increase of temperature, although new 

 ones may be rendered visible. 



In these memoirs, and also in others ' On Phosphorescence,' and 

 ' On the Chemical Action of Light,' subsequently published, there is 

 a multitude of facts and observations, full of interest, but too numerous 

 to quote in this abstract. Among such, perhaps, I might mention the 

 Chlorine and Hydrogen Photometer, subsequently used so extensively 

 by MM. Bunsen and Roscoe, and the attempt to show that the Fraun- 

 hoferian lines are arranged in a certain symmetrical order, herein to 

 some extent anticipating the remarks of Professor Hinrichs, before 

 referred to. It should also be added that many other experiments in 

 Photo-Chemistry were published by Dr. Draper, in a quarto volume 

 of 324 pages, illustrated by engravings, under the title of ' A Treatise 

 on the Forces that produce the Organization of Plants.' 



Mr. L. M. ButherfurcVs experiments. — ' Silliman's Journal,' Nos. 

 ciii., 1863; cv., 1863; cvi., 1863. In December, 1862, Mr. Ruther- 

 furd determined to continue Fraunhofer's experiments on stellar spectra 

 by means of a refracting telescope of 11 J- inches aperture, mounted 

 equatorially, and driven by a clock. He used at first an ordinary 

 spectroscope, with the slit inside the focus of the large achromatic, 

 but finding the loss of light upon the jaws of the slit to be very great, 

 eventually employed a cylindrical lens, as Fraunhofer had done. This 

 also frees the spectrum from longitudinal lines. He observed that a 



