NATUKAL PHILOSOPHY. 143 



margin of the flame, and could be curved or twisted about in any direction, 

 at the will of the experimenter, giving a perfect illustration of the crooked 

 form of lightning, and of the probable reason why it does not pass in straight 

 lines the temperature of the air being different at different points in its pas- 

 sage, and much of this variation of temperature being in all probability oc- 

 casioned by the mechanical effects of the discharge itself upon the air. 



TELOCITY OF THE ELECTRIC CURRENT. 



h 



M. Quetelet, at a recent meeting of the Belgian Academy, described Mr. 

 Airey's experiments with the electric telegraph to determine the difference 

 of longitude between Greenwich and Brussels. The tune spent by the electric 

 current in passing from the one observatory to the other was found to be 

 0.1 09" or rather less than the ninth part of a second, and this determination 

 rests on 2,616 observations. The distance between the towns being 270 

 miles, the velocity of the current, supposing it to be uniform, must rather ex- 

 ceed 2,500 miles per second, or about one seventh greater than that obtained 

 by the American observers, a speed which would "girdle the globe" in ten 

 seconds. The difference of longitude from two series of observations, and by 

 two methods, "was found to be 17'28.9" Observations made by an eclipse 

 of the sun in May 1836, gave precisely the same results, which may be con- 

 sidered the most correct. An eclipse of the sun in 1842 gave four tenths of a 

 second less ; lunar occultations gave nine tenths of a second less ; and observ- 

 ations by chronometers gave one second and three tenths less. A second in 

 this case represents a distance of 455 yards, and a tenth of a second 454- yards. 

 Assuming the first-mentioned time to be correct, the error in the chron- 

 ometrical determination is equivalent to 591 yards, or the ninth part of a 

 mile, which, after all, is only the 2430th part of the whole distance. 



THERMO-ELECTRIC CURRENTS. 



A number of interesting experiments on the construction of thermo-electric 

 batteries have recently been conducted by Mr. Adie, of England, the object, to 

 a certain extent, being to test the direction of the electric current hi relation 

 to that in which the heat passes. In the first instance a bismuth joint was 

 formed by soldering together two bars of the same metal 7 2 pairs of plates 

 being thus connected. "When gold, silver, platinum, copper, zinc, cadmium, 

 antimony, iron, or soft steel, were employed, the electric current flowed hi an 

 opposite direction to that of the heat. "When palladium, lead, and tin were 

 used, the direction of both currents was the same. When two bars, each of a 

 different metal, soldered together by bismuth, were acted on, the results were 

 various. In 28 pairs the direction of the heat current was opposed to the 

 electric ; in one pair composed of lead and tin, the heat and electricity crossed 

 the joint in the same direction; in 31 cases the pairs acted according to their 

 thermo-electric relations, independent of the side joint to which the heat was 

 applied. There were only four cases hi which the heat and electricity coursed 

 in the same direction, and in these the peculiarity was attributed to the tend- 



