1869.] Phjsics. 147 



so suitable ; and not only did the perfect symmetry of the exterior 

 suggest this idea, but the exquisite casing and folding of film within 

 fihn suggested the internal economy of a highly complex organism. 

 The hvoness of the animal form was displayed throughout, and no 

 coil, disk, or speck existed on one side of the axis of the tube that 

 had not its exact counterpart at an equal distance on the other. I 

 looked in wonder at this extraordinary production for nearly two 

 hours." 



It will be remembered that six or seven years ago Dr. Frank- 

 land communicated to the Eoyal Society some researches on the 

 effect of a diminution of pressure on some of the phenomena of 

 combustion, and deduced therefrom the law that the diminution in 

 illuminating power is directly proportional to the diminution in 

 atmospheric pressure. Further experiments on the nature of the 

 luminous agent in a coal-gas flame have led him to doubt the cor- 

 rectness of the commonly received theory first propomided by Sir 

 Humphi-y Davy, that the light of a gas flame and of luminous 

 flames in general, is due to the presence of solid particles. It has 

 been found that there are many flames possessing a high degree of 

 luminosity, which cannot possibly contain solid particles, such as 

 the flame of metalhs arsenic burning in oxygen, which emits a 

 remarkably intense white hght ; bisulphide of carbon in oxygen ; 

 and especially phosphorus in oxygen. 



For these reasons, and for others which the author had stated 

 in a course of lectures on " Coal-gas," delivered in March, 1867, he 

 considered that incandescent particles of carbon are not the source 

 of hght in gas and candle flames, but that the luminosity of these 

 flames is due to radiations from dense but transparent hydrocarbon 

 vapours. As a further generalization from the above-mentioned 

 experiments, he was led to the conclusion that dense gases and 

 vapours become luminous at much lower temperatures than aeriform 

 fluids of comparatively low specific gravity ; and that this result is 

 to a great extent, if not altogether, independent of the nature of the 

 gas or vapour, inasmuch as he found that gases of low density, 

 which are not luminous at a given temperature when burnt under 

 common atmospheric pressure, become so when they are simul- 

 taneously compressed. Thus mixtures of hydrogen and carbonic 

 oxide with oxygen emit but little light when they are burnt or 

 exploded in free air, but exhibit intense luminosity when exploded 

 in closed glass vessels, so as to prevent their expansion at the 

 moment of combustion. 



In a communication to the Eoyal Society, Dr. Frankland has 

 described the extension of these experiments to the combustion of 

 jets of hydrogen and carbonic oxide in oxygen under a pr&ssure 

 gradually increasing to twenty atmospheres. These experiments 



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