548 Intelligence and Miscellaneous Articles. 



If it be received on the screen, it appears as a bright spot on a 

 feebly luminous ground, and changes after a lengthened action into 

 a black spot, which has the same appearance as if a hole had been 

 bored in a bright surface. 



Instead of a solution of iodine or bisulphide of carbon, both 

 which substances have their drawbacks, I use a solution of nigro- 

 sine in chloroform or alcohol. These solutions are quite black 

 and only transmit ultra-red rays. Alcohol, it is true, strongly 

 absorbs the ultra-red rays, so that the alcoholic solution only gives 

 a focus of small thermal action. This fact is. however, advantageous 

 for the above experiment ; for the luminosity of the very sensitive 

 phosphoescent substance lasts longer, and the blackening does not 

 set in so rapidly, as if the focus were more intense. The far more 

 diathermanous solution in chloroform gives a sufficiently hot focus 

 for demonstrating the thermal action ; nigrosine is insoluble in the 

 still more diathermanous bisulphide of carbon. 



With the great sensitiveness of phosphorescent substances for 

 ultra-red rays, the flame of gas, of a lamp, or even a candle is 

 sufficient to show the phenomenon. By means of the spherical 

 flask, or, still better, by means of a lens with interposition of a 

 plane parallel trough filled with the black liquid, a sharp bright 

 (positive) image of the flame is received on the screen ; after the 

 radiation has ceased this lasts with continually decreasing intensity, 

 and then turns into a dark (negative) image on a brighter ground. 

 This is a kind of photography by means of invisible ultra-red rays. — 

 Wiedemann's Annalen, No. 9, 1885. 



ON THE TONES PRODUCED IN A PLATE OR A COLUMN BY FREQUENT 

 DISCHARGES OF AN ELECTRICAL MACHINE. BY E. SEMMOLA. 



The conductors of an induction machine are connected, by means 

 of two wires 5 metres in length, with two binding-screws fixed at 

 the opposite sides of a brass plate 1 millim. in thickness, which rests 

 on an ebonite funnel. If, now, the path of the current is broken 

 so that sparks strike across, the brass plate begins to sound. It 

 sounds also even if a Greissler's tube or a lead wire is interposed in 

 the break ; and also if iu stead, a wire is led to earth from the one 

 binding-screw, and in this a break is made. If the end of the 

 broken wire is so far removed from the binding-screw that sparks 

 pass, the tone is stronger, and can be distinctly discriminated from 

 the sound of the sparks. 



Even if the wires are connected with a metal plate which stands 

 opposite that on the hearing-apparatus, sounds are heard in the 

 last-mentioned experiments. If the plate on the hearing-tube is 

 connected with the earth, the note is stronger. The same is also 

 slightly the case when a glass plate is interposed. If the wire 

 leading to earth is not broken, no sound is heard. 



If the w'ires are connected with the insulated wire of a sonometer 

 instead of with the brass plate, nothing is heard ; if, however, an 

 ebonite ear -trumpet is placed on the box the sound is audible. — 

 Beibldtter der PhysiJc, vol. ix. p. 671. 



