071 the iise of the Multiplying Bheometer. 4-23 



ments mentioned in the Guide, and the results be communi- 

 cated to some scientific body. 



With regard to the remarks on the November wave by the 

 writer oF the notice, I am quite of opinion that the movements 

 I have observed are not confined by any means to November, 

 nor do they extend only to the three autumnal months, but 

 are to be detected in every month all the year round. Nor 

 do I apprehend that these movements stand out more promi- 

 nently in November than at any other time. The only reason 

 that they have been brought more prominently into notice in 

 November is, that more attention has been paid to the baro- 

 metric phsenomena in that montli. The mode of inquiry isj 

 however, one involving considerable labour, and requiring 

 numerous stations ; so that unless a gentleman is able to de- 

 vote to it the whole of his time, or at least a very considerable 

 portion of it, the progress in the general investigation must be 

 but slow. Some of the most valuable data would be obtained 

 from marine observations. 



I have the honour to be, my dear Sir^ 



Yours Very respectfully, 



W. R. BiRT. 



LIV. Eighth Memoir on Induction. J5z/M.ElieWartmann^ 

 Professor of Natural Philosophy in the Academy of Geneva"^. 

 [Continued from vol. xxxiii. p. 446.] 



§ XX. On the use of the mtdtiplying Rheometerfor measuring 

 differences of intensity ofvoeak or powciful Electric Currents. 



211. ^I^HE measure of the variations of intensity of galvanic 

 JL currents is ordinarily effected by the aid of the vol- 

 tameter. But the employment of this apparatus requires 

 various precautions, without which we arrive at false results, 

 and diminishes the energy of the current by the whole of the 

 resistance proceeding from the liquid under decomposition. 

 it is often more convenient to employ the galvanometer, which 

 does not expose us to the same errors. I do not speak of the 

 coarse multipliers with a single very heavy needle, such as 

 were constructed twenty years ago, but of rheometers with a 

 longer or shorter wire, and furnished with an almost astatic 

 system of light needles delicately suspended. 



212. If the current which has to be appreciated is suffi- 

 ciently weak not to heat a thin copper conductor, it is distri- 

 buted between the two equal wires of a differential galvano- 

 meter, giving it an opposite direction in each of them, or the 



* From the Bibliotheque UniverseUe de Geneve, January 1850. 



