108 ANNUAL OF SCIENTIFIC DISCOVERY. 



lines stand out upon the comparatively uniform ground of the solar 

 spectrum, so that it might be seen that, notwithstanding their appar- 

 ently accidental grouping, they all possessed the tint of color corre- 

 sponding to their refrangibility. But what is peculiar in this experi- 

 ment is, that among these electric lines some possess an intensity enor- 

 mously superior to that of the corresponding solar ray. Especially 

 in the arc from silver there is a green ray, so to speak, inextensible 

 by the prisms, and of a dazzling color. It is a true source of simple , 

 light, and as it is insulated, and as the arc from silver is transparent, 

 tranquil, and durable, there is nothing to prevent this ray from being 

 made the source of a green light as intense as may be wanted, and 

 from being utilized for the demonstration of phenomena heretofore in- 

 dicated by theory alone. Other very intense rays have also their 

 fixed places in different parts of these spectra and even at their ex- 

 tremities, and there is great probability of discovering isolated lines, 

 the rays corresponding to which cannot be seen in the solar light." 

 L'lnstilut, Feb. 7. 



POLARIZATION OF GALVANIC LIGHT. 



PROFESSOR C. G. PAGE, of the Patent-Office, has communicated to 

 Sittiman's Journal, No. 21, a paper on this subject. "Having seen it 

 stated, upon the authority of Arago, that the light of the galvanic 

 arc, like that from incandescent gas, was not polarizable, I have been 

 induced to repeat the experiment, with a view of testing, for my own 

 satisfaction, a principle so important in a theoretical point of view. 

 The experiment was briefly performed, and only with reference to the 

 simple fact itself. The battery employed was a Grove's, of fifty 

 pairs platinum plates, four inches square, and double surface of zinc. 

 By means of a Nicols prism, and one reflection from a plate of mica, 

 the light from the arc between the charcoal points w r as distinctly 

 polarized. Its property in this respect was much more decided 

 when the arc was first formed than when it had continued for a few 

 seconds. It may be observed, that when the electrodes are first with- 

 drawn the arc is very intense, arid does not rise in the arched form 

 immediately, but as soon as the charcoal points have become intense- 

 ly heated, the arc becomes elongated and rises, from the upward cur- 

 rent of air, and the upper portion of the arc is then feeble in intensity. 

 This upper portion did not appear at all polarizable upon a single re- 

 flection, but upon two reflections was decidedly so." 



VOLTAIC IGNITION. 



THE following is an abstract of a paper recently read before the 

 Royal Institution (England), on " Voltaic Ignition," by Mr. Grove, 

 well known for- his researches on electricity and galvanism. Mr. 

 Grove introduced the subject by asserting that the only true philo- 

 sophical idea of heat W 7 as that which regards it as a repulsive power, 

 that with the single exception of water, and other bodies which 

 assume a crystalline form when about to freeze (a condition which he 



