476 Intelligence and Miscellaneous Articles. 



Although these determinations were only of a preliminary 

 character, and the bottle from which the acid was supplied 

 was graduated but roughly, yet the breaks shown by the 

 results are in perfect agreement with those indicated by my 

 former work. Fig. 1 shows breaks at 0*08 and 0'38 per cent. 

 of acid (allowing for the one-minute lag of the thermometer) , 

 and fig. 2 places the latter at 0*33 per cent., mean 0*355 : 

 whereas my heat of dissolution determinations gave breaks at 

 0*1 and 0*4 per cent. (loc. cit. p. 127), and the most probable 

 positions of these, as deduced from the freezing-points and all 

 the other properties examined together (loc. cit. p. 352), were 

 0*087 and 0*345 per cent, respectively. 



XLIII. Intelligence and Miscellaneous Articles. 



MEASUKEMENTS WITH ALTERNATING CURRENTS OF HIGH 

 FREQUENCY. BY DR. JOSEF TUMA. 



rPHE author determines the resistance of copper, german silver, 

 -*- nickel, and iron wires for oscillating currents. He uses two 

 Bunsen ice-calorimeters with thin glass tubes passing completely 

 through them instead of test-tubes. In the tube of one calori- 

 meter is introduced the piece of wire to be investigated, and in the 

 other a resistance constructed of a thin (0-001 — 0*010 millim.) 

 tubular layer of silver or copper deposited on glass. 



By preliminary experiments it is ascertained that the alternating 

 currents used (84,400 — 232,900 oscillations in a second) have the 

 same density of current throughout the whole section. Alterna- 

 ting currents are sent through the two calorimeters arranged in 

 series, or steady currents for the purpose of graduation, and from 

 every two pairs of such readings the strength of the alternating 

 current and the ratio w'/iv of the resistances of wires for alterna- 

 ting and steady currents were measured. 



Values were obtained which only approximately agree with the 

 formulas developed by Stefan, for they presuppose far higher num- 

 bers of vibrations than those used here. The author could not 

 produce such rapid vibrations, for it was necessary to add to the 

 short wires to be measured a high calculable self-induction ; other- 

 wise the number of vibrations wou'd vary according to the resist- 

 ances to be determined, and they would moreover be very difficult 

 to calculate. It could always be seen that, for alternating currents 

 of high frequency, the agreement was more complete for non- 

 magnetizable conductors. For magnetic substances calculations 

 are illusory, owing to the variability of the permeability. The 

 author observed in the case of iron wires that the resistance varied 

 with the strength of the alternating current, decreasing as the 

 current increased. — Wiener Berichte, June 14, 1895. 



