Thermomagnetic Properties of Crystalline Bismuth, 141 



would fail to disturb greatly the state of things that would 

 prevail, were every parallel of latitude barred. I£ this con- 

 clusion be admitted, the theoretical fortnightly tide will not 

 differ materially from its equilibrium value, and Darwin's 

 former calculation as to the earth's rigidity will regain its 

 significance. 



Some caution is required in estimating the weight of the 

 argument above adduced. Though there were no free dis- 

 turbance possible o£ infinitely long period, it would come to 

 the same, or to a worse, thing if free periods existed com- 

 parable with that o£ the forces, which is itself by hypothesis 

 a long period. On this account a blocking of every parallel 

 of latitude by small detached islands would not suffice, 

 although meeting the theoretical requirement of the limiting- 

 case. 



It would serve as a check and be otherwise interesting if 

 it were possible to calculate the fortnightly tide for an ocean 

 of uniform depth hounded by two meridians. The solution 

 must differ widely from that appropriate to an unlimited 

 ocean ; but, although the conditions are apparently simple* 

 it does not seem to be attainable by Laplace's methods. A 

 similar solution for the semi-diurnal tide would be interesting 

 for other reasons. 



In any case I think that observations and reductions of 

 the fortnightly tide should be pursued. Observation is com- 

 petent to determine not merely the general magnitude of 

 the tide but the law as dependent upon latitude and longi- 

 tude. Should the observed law conform to that of the 

 equilibrium theory, it would go a long way to verify 

 a posteriori the applicability of this theory to the circum- 

 stances of the case. 



VIII. The Thermomagnetic and Related Properties of Crystal- 

 line Bismuth. By Louis Lownds, B.Se. (Loud.), Ph.D. 

 (Berlin), 1851 Exhibition Research Scholar, Univ. Coll.. 

 Nottingham*. 



§ 1. A FORMER paper, published in the Philosophical 

 J\ Magazine for October 1901, gave an account of 

 the Longitudinal and Transversal Thermomagnetic Effects 



of Bismuth 



ci 



and the Thermoelectric Properties of a Plate of Bismuth 



iut from a crystal of the metal in the pos>o>sion of Prof. 



Groth of Miinchen. The present contains an account 



of the investigation of the change of electrical resistance 



* Communicated by the Author. 



