294 Intelligence and Miscellaneous Articles. 



cobalt with a bismuth plate by simultaneously heating them on 

 one side, and cooling on the other while separated from each other 

 by a plate of mica, and placed in the magnetic field. The ratio of 

 the thermomagnetic effects referred to Bi=100, were for Sb= 5*5, 

 for m 4-8, and for Co = 0-5. 



In how far the observed currents can be brought in connexion 

 with Hall's phenomenon must for the present be left undecided. 

 We may be allowed to mention that Sb, Co, Fe, and steel have a 

 positive rotatory power, Bi, and Ni, on the contrary, a negative 

 one, which is in agreement with our own measurements of the 

 Hall's phenomenon in the plates in question, although our numbers 

 differ greatly from those of Hall. 



If the bismuth plate previously mentioned was traversed by a 

 galvanic current, then in order to produce in the same magnetic 

 field a Hall's electromotive power of the same strength as the 

 thermomagnetic which we observed, it must have an intensity of 15 

 amperes, assuming the same intensity in all parts of the plate. 



This phenomenon appears in any case to be ultimately related 

 to the molecular structure of the metals. — Wiedemann's Annalen, 

 No. 10, 1886. 



ON THE EXPERIMENTS MADE AT THE INSTANCE OF THE ELECTRO- 

 TECHNICAL UNION ON THUNDER-STORMS AND PROTECTION 

 AGAINST LIGHTNING. BY L. WEBER. 



In order to investigate the influence of the efficiency of lightning- 

 conductors, the author arranged two lightning-conductors, about 

 6 metres high, which carried the various points, about 5 metres 

 from each other, and introduced a galvanometer into the earth- 

 contact. Experiments made with this arrrangement in various 

 places in the Biesengebirge, as well as in Breslau and the neigh- 

 bourhood, showed the applicability of the method. Observations 

 were also made on the increase of potential with the height. A 

 kite, the conducting-cord of which was connected with a galvano- 

 meter, was allowed to rise to various heights near a detached house 

 in the vicinity of Breslau, and the following results were obtained : — 



Height, in metres .... 45 71 107 140 115 78 41 139 

 Strength of current .... 29 61 451 1078 627 257 40 1332 



The unit of current is 10 ~ 9 amperes. At the beginning of the 

 observations the sky was covered with light cirrostratus clouds; 

 towards the end it cleared up. The observations agree with those 

 of Exner, found by electroscopic means (Beibl'dtter, vol. xi. p. 292). 

 Some experiments were also made during the passage of clouds, 

 which sometimes showed their negative electricity. In thunder- 

 storms the galvanometer shows a momentary agitation, which cor- 

 responds to a return shock in the lightning-conductor. The needle 



