226 Intelligence and Miscellaneous Articles, 



porphyry and trachytic rocks, of which the former contains 75 1 

 and the latter 61 per cent, of silica. 



The clays from which the shales were originally formed contain 

 abundance of marine Diatom aceae and Eoraminifera (chiefly Num- 

 mulites), as also species of Ostrea, Cyrena, Cerithium, Voluta, and 

 Nautilus, together with the remains of Placoid and Teleostean fishes. 



XXVII. Intelligence and Miscellaneous Articles. 



ON SOME EXPERIMENTS RELATING TO HALL S PHENOMENON. 

 BY PROF. BOLTZMANN. 



T^EOM the general equations which Maxwell and Eowland had 

 -*- given for the movement of electricity, Lorentz (Wiedemann's 

 Beiblatter, viii. p. 869) deduced the following equations for the 

 movement of electricity in a plane plate at right angles to the lines 

 of force of a magnetic field, provided that the Hall's deflection of 

 the current by magnetism is taken into account : 



u= — K-f- — hv, v = —K-±--\-hu; 



ax ay 



u, v, p, k are the components of the current, the electrical tension, 

 and specific conductivity, and h a constant which is probably nearly 

 proportional to the strength of the magnetic field. From these 

 equations I have deduced certain conclusions which seem to me 

 worthy of being experimentally tested. The following integral 

 corresponds to Hall's observations : 



p=—ax+hay, u = kc(, v = 0. 



In an iron strip with the bounding lines y = and y = b, and the 

 thickness £, a current J = nabs flows in the direction OX. The 

 north pole is on the positive Z side. The hands of a watch the 

 face of which is turned towards OZ, run from OX towards OY. 

 In a Hall circuit, which from its great resistance does not mate- 

 rially alter the condition of the strip, a current is driven by the 

 electromotive force e=hab, which flows in the iron strip, against 

 the positive ^/-direction. By rotatory power E Hall understands 

 the quotient «S/JM, so that 7i =EMa\ I may observe that the 

 absolute values which Hall gives for E are far too small ; possibly 

 owing to a confusion of the ohm with the resistance-unity they 

 should be multiplied by 10 9 . From the above equations follows : 



u + hv=—K^-, u=—k(^- — h c JP\ 



ax \ax ay J 



v -n u =-A, v=-Tc( d JL+n d J>\ 



ay \dy ax J 



in which Tc=k : 1+h 2 . The equation of continuity, 



du dv ~ 



due dy 



