Intelligence and Miscellaneous Articles. 125 



The action of the bismuth in the open air will be explained if we 

 remember that both the iron and the bismuth are surrounded by a 

 mass of magnetized air, so that the behaviour of the bismuth is due 

 to three causes : — 



(1) The attraction of the iron magnet. 



(2) The attractions of the magnetized atoms of air. 



(3) The resultant of the unequal pressures of the air over the 

 surface of the bismuth. 



The conclusions of this paper naturally lead us to question the 

 propriety of making our " absolute " units of electricity and mag- 

 netism depend on the actions between bodies surrounded by elec- 

 trified or magnetized air about which all that is known is that, at 

 some distance away, the air with which it is in equilibrium has a 

 measurable pressure. 



AN EASY MODE OF PRODUCING THE ACTIVE SPAKK IN HERTZ S 

 EXPERIMENTS. BY H. CLASSEN. 



In repeating Hertz's experiments in the State Physical Laboratory 

 at Hamburg, an observation was made which shows how in a simple 

 manner we can overcome the difficulty experienced by many ob- 

 servers of keeping the primary spark effective for a long time 

 together. In the same manner in which Eijke* used the action of a 

 current of air on the make-and-break spark of an induction-coil in 

 order to produce a stronger action in the secondary coil, so may 

 the spark of the coil itself, and therefore also its inductive action 

 on any other conductor, be similarly influenced. 



In the experiments a large Euhmkorff's coil was used which had 

 a very rapid contact-maker, and which gave sparks up to 14 ceutim. 

 If the ends of the secondary coil are loaded with conductors, and 

 the discharging-knobs are brought within a distance of a few centi- 

 metres, the discharge takes place mostly in the form of a continuous 

 rose-coloured strip of light, and is useless for Hertz's experiments. 

 But when this band is blown away so that flames a centimetre in 

 length project on the side, sharp brightly luminous sparks occur 

 between the knobs. The current of air produced by a Miinke's 

 water-pump was now blown continuously between the knobs, and 

 thus a series of sharp cracking sparks passed quite continuously, 

 and could without difficulty be continuously maintained for hours. 

 A series of Hertz's experiments could now be repeated, and even 

 when the current of air was replaced by one of steam the action 

 was the same. The whole process suggests the idea that, in the 

 ordinary discharge with a luminous band of light, detached metallic 

 particles effect a permanent conduction, and that the essential 

 discharge-spark is only produced as these particles are blown away. 

 The influence of the ultra-violet illumination, too, which has been 

 designated by various observers as highly disturbing, would, after 

 the researches of Lenard and "Wolf on the pulverization of bodies 



* Pogg. Ann. cxvii. p. 276 (1862). 



