British Association for the Advancement of Science. 299 



On the Prismatic Decomposition of Electrical Light. By Professor 

 Wheatstone. 



The following is a brief notice of the principal results stated in this 

 communication: 1. The spectrum of the electro-magnetic spark 

 taken from mercury consists of seven definite rays only, separated 

 by dark intervals from each other ; these visible rays are two orange 

 lines close together, a bright green line, two bluish green lines 

 near each other, a very bright purple line, and, lastly, a violet line. 

 The observations were made with a telescope furnished with a mea- 

 suring apparatus ; and to ensure the appearance of the spark inva- 

 riably in the same place, an appropriate modification of the electro- 

 magnet was employed. 2. The spark taken in the same manner 

 from zinc, cadmium, tin, bismuth, and lead, in the melted state, 

 gives similar results; but the number, position, and colours of the 

 lines varies in each case ; the appearances are so different, that, by 

 this mode of examination, the metals may be readily distinguished 

 from each other. A table accompanied the paper, showing the po- 

 sition and colour of the lines in the various metals used. The 

 spectra of zinc and cadmium are characterized by the presence of a 

 red line in each, which occurs in neither of the other metals. 3. When 

 the spark of a voltaic pile is taken from the same metals still in the 

 melted state, precisely the same appearances are presented. 4. The 

 voltaic spark from mercury was taken successively, in the ordinary 

 vacuum of the air-pump, in the Torricellian vacuum, in carbonic 

 acid gas, &c, and the same results were obtained as when the expe- 

 riment was performed in the air or in oxygen gas. The light, there- 

 fore, does not arise from the combustion of the metal. Professor 

 Wheatstone also examined, by the prism, the light which accompa- 

 nies the ordinary combustion of the metals in oxygen gas and by 

 other means, and found the appearances totally dissimilar to the 

 above. 5. Fraunhofer having found that the ordinary electric spark 

 examined by a prism presented a spectrum crossed by numerous 

 bright lines, Professor Wheatstone examined the phenomena in dif- 

 ferent metals, and found that these bright lines differ in number and 

 position in every different metal employed. When the spark is taken 

 between balls of dissimilar metals, the lines appertaining to both are 

 simultaneously seen. 6. The peculiar phaenomena observed in the 

 voltaic spark taken between different metallic wires connected with 

 a powerful battery were then described, and the paper concluded 

 with a review of the various theories which have been advanced to 

 explain the origin of electric light. Professor Wheatstone infers 

 from his researches, that electric light results from the volatilization 

 and ignition (not combustion) of the ponderable matter of the con- 

 ductor itself; a conclusion closely resembling that arrived at by 

 Fusinieri from his experiments on the transport of ponderable mat* 

 ter in electric discharges. 



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