Nov. 14, 1878] 



NATURE 



Z7 



larly on the whole than the maxima and minima of sun- 

 spots. 



But -why do we beat about the bush when all that is 

 needed is half-a-dozen of Pouillet's pjTheliometers with 

 skilled observers, who will seize every clear day to deter- 

 mine directly the heating power of the sun? Why do 

 we not go direct to the Great Luminary himself, and ask 

 him plainly whether he varies or not? If he answers 

 No ! then some of us must reconsider our theories, and 

 perhaps endure a little ridicule. But if, as is much more 

 probable, he should answer Yes ! then the time will come 

 when the most important news in the Times wnll be the 

 usual cablegram of the solar power. Solar obser\"atories 

 ought to be established on the table-lands of Quito or 

 Cuzco, in Cashmere, in Piazzi Smyth's observatory on the 

 Peak of Teneriffe, in Central Australia, or wherever else 

 the sun can be observed most free from atmospheric 

 opacity. An empire on which the sun never sets, and 

 whose commerce per\-ades ever>' port and creek of the 

 sunny south, cannot wisely neglect to keep a watch on the 

 great fountain of energy. From that sun, which is truly 

 '* of this great world both eye and soul," we derive our 

 strength and our weakness, oiu- success and our failure, 

 our elation in commercial mania, and our despondency 

 and ruin in commercial collapse. 



W. Stanley Jevons 



THE WERDERMANN ELECTRIC LIGHT 



"\X/^E are able this week to give some further details 

 ' ' concerning Mr. Werdermann's method of dividing 

 the electric light. 



The real difficulty was foimd in devising a form of 

 light which could be di\-ided into several, and still give 

 enough illuminating power for practical use ; and it is in 

 this particular that Mr. Werdermann has apparently 

 succeeded. It may be interesting here to state Mr. 

 Werdermann's reasons for adopting this particular form 

 of lighting. 



When in an electric lamp, electrodes having the same 

 sectional area are used, the changes at the points between 

 which the voltaic arc passes, take place in a manner which 

 is well known, viz., a crater or hollow is formed in the 

 positive electrode which emits the light, the crater itself 

 being heated by the current to white heat, and the sur- 

 roimding part to redness. The negative electrode which 

 assumes the form of a cone, is only heated to redness, 

 and emits scarcely any light. 



It was found that an increase in the sectional area of 

 the positive electrode diminishes the light emitted by that 

 electrode, and if the increase is continued gradually, the 

 light on that electrode finally disappears entirely, where- 

 as the heating effect upon the negative electrode in con- 

 nection therewith increases, until finally light is emitted 

 by the same. Again, by increasing the sectional area of 

 the negative electrode, the heating effect upon the same 

 decreases proportionaUy to the increase of its area, until 

 the area ha\ing been sufficiently increased the heat 

 almost entirely disappears, and consequently the con- 

 sumption or wearmg away of that electrode is scarcely 

 appreciable. 



The light given out by the positive electrode in connec- 

 tion therewith, on the contrarj', increases in proportion to 

 the difference existing between the sectional area of the 

 two electrodes, and instead of a crater being formed in 

 the positive carbon, the latter assumes the form of a cone 

 as formerly was the case with the negative carbon. The 

 greater the difference between the areas of the two 

 carbons the shorter is the length of the voltaic arc which 

 can be obtained between them, and when the area of the 

 positive is gradually diminished and that of the negative 

 increased, the light is produced by the carbons apparently 

 m contact, and a small deposit of graphite is seen on the 



negative electrode. The section of this deposit is about 

 \ that of the positive carbon itself, and it is about \ of an 

 inch high. 



Mr. Werdermann was led to make these experiments 

 by the idea that perhaps by altering the sectional area of 

 the carbons a similar effect might be produced to that 

 which is obtained in electrolysis when a plate is used as 

 one electrode and a small wire at the other, and from the 



Fig. 



results obtained he devised his present system of electric 

 lighting. 



His lamp is constructed in the following manner : — 

 He places the negative carbon which is in the form (rf 

 a disc 2 inches in diameter, and about i inch thick, 

 uppermost This carbon is clasped all roimd by a copper 

 band which is prolonged to the terminal to which one of 

 the leading cables is attached. The lower or positive 

 electrode is a small pencil of carbon 3 millimetres in 



Fig. 2. 



diameter, and can be made of any suitable length. This 

 slides up vertically in a tube placed directly imdemeath 

 the disc. This tube guides the pencil and also forms a 

 contact for it, the top of the tube being solid copper in 

 two pieces, one being rigid and the other pressing against 

 the carbon by means of a regulating spring. The carbon 

 pencil protrudes above the tube about | of an inch, and 

 touches the negative disc, and this length when the 

 current passes is made incandescent. 



