On the Longitudinal Lines of the Solar Spectrum. 347 



found to be, that a blackish powder* was deposited on the zinc 

 which partially defended it from further action. When this 

 powder was removed and the plate replaced, the needle stood at 

 the original degree, but soon fell again owing to the same cause. 



It is to be observed, that in the foregoing experiments the 

 same results may not be obtained if the same strip of copper be 

 used more than once, the cause of which will be found in my 

 " Essay on the Origin, Progress, and Present State of Galva- 

 nism," p. 288. 



The term made use of in the enunciation of Faraday's law is 

 " absolute quantity of electricity." The word absolute, perhaps, 

 implies that the quantity is not restricted by the condition of 

 intensity. If the idea of totality be involved, the expression can 

 only apply to the discharge of the Leyden battery. When voltaic 

 electricity is in question, no part of it can be considered active 

 but that which is at any particular moment in the coil, without 

 reference to the portion already passed through or yet to arrive, 

 which latter may be said not yet to exist as the zinc is not yet 

 dissolved. Hence the galvanometer can never be influenced by 

 the whole quantity that is to pass ; it indicates things present, 

 not future. 



If these experiments and reasonings be correct, and I do not 

 perceive any source of fallacy, they appear unconformable to 

 Faraday's law of equal quantities of electricity producing equal 

 deflections irrespectively of other circumstances. Support is 

 consequently withdrawn from his estimate of the enormous 

 quantity of electricity naturally associated with matter, an esti- 

 mate founded on his experiment in which the voltaic action of a 

 pair of wires, acted on by acid, is said to have evolved electricity 

 equal to 300 or 360 dense sparks from a powerful electric 

 machine in the short space of -j-^ths of a minute. 

 [To be continued.] 



XLIX. On the Longitudinal Lines of the Solar Spectrum. From 



a Letter to Professor Dove by Professor Ragona-Scinat. 



[With a Plate.] 



HERETOFORE the longitudinal lines of the solar spectrum 

 have attracted little attention. It was believed by phy- 

 sicists that they were due to the minute imperfections of the 

 glass of the prism, the little irregularities along the edge of the 



* "Most zincs, when put into dilute sulphuric acid, leave more or less of 

 an insoluble mattes upon the surface in the form of a crust, which contains 

 various metals, as copper, lead, zinc, iron, cadmium, &c, in the metallic 

 Rtate. Such particles, by discharging part of the transferable power, render 

 it, as to the whole battery, local, and so diminish the effect." ( Faraday, 1 144.) 



t Prom Poggendorff's Annalen, vol. lxxxiv. p. 590. 



