160 Intelligence and Miscellaneous Articles. 



bulb of the thermometer, acted as a surface O heated to near 100°, 

 the enclosure being at 9 C, 2. The total intensities of the three 

 radiations sent to the thermometer by the surfaces S, w, and 11 were 

 then sensibly proportional to the numbers 15, 1, and 0*1. 



It will not be uninteresting, and I have already some measure- 

 ments on this point, to compare at different periods, and especially 

 at different altitudes, the radiation of this portion of the sky bor- 

 dering the sun, the illumination of which exhibits at times remark- 

 able intensity. Perhaps we shall find there a portion of the heat 

 lost by the direct rays in their passage through our atmosphere. — 

 Coniptes Mendus de TAcad. des Sciences, May 18, 1874. 



ON A PECULIAR PHENOMENON IN THE PATH OF THE ELECTRIC 

 STARK. BY PROF. TOEPLER, OF GRAZ. 



It is well known that the sparks from the discharge of a Leyden 

 jar leave upon the surfaces of insulators a trace, conditioned by cer- 

 tain mechanical processes. The phenomenon is especially charac- 

 teristic upon very delicately smoked glass surfaces to which sparks 

 spring between pointed conductors. I have therein observed a re- 

 gular microscopic structure. 



With a length of spark of 4 to 6 centims. the trace is generally 

 a bright streak 3 millims. wide, with a dark axis, produced by the 

 soot-particles being partly thrown to the sides, partly going to 

 the axis and there accumulating. On this trace there is further 

 found a mostly very striking knot-like thickening just where the 

 lateral motion ol the air has taken place with peculiar violence — a 

 place in the spark which had already struck me in my optical 

 observations (Pogg. Ann. vol. cxxxiv.). Before this spot the 

 trace is altogether different from what it is beyond. Towards 

 the positive conductor the spark-path is mostly branched off like 

 a tuft, towards the negative not so. "When the trace is ex- 

 amined with a magnifving-power of 15-20, there appears fre- 

 quently on the positive side, never on the negative, in the dark 

 axis of the spark-path a very fine dark zigzag line resembling a mi- 

 croscopic sine-curve, of 0-12-O13 millim. wave-length. From the 

 internal angles of this line issue laterally equidistant bright streaks 

 inclined to the axis of the spark in the direction of motion of the 

 positive electricity. This microscopic structure (the regularity of 

 which is sometimes surprising) is often found also just as distinct 

 on the fine side branches which break forth from the positive part 

 of the spark-path. I remark, further, that the soot-particles which 

 exhibit the structure are in some measure fixed to the glass surface ; 

 for when the layer of soot is removed, say, with a fine hair pencil, 

 the dark streak in the axis of the spark remains adhering, though 

 of course the microscopic delicacy of the figure is destroyed. — 

 Sitzung der maih.-naturw. Classe der Tcaiserl. AJcad. d. Wissensch. in 

 TFWMay 15, 1874. 



