Prof. Grove on the Gas Voltaic Battery, 377 



He proceeds to consider, in the remaining part of his paper, the 

 application of the gas battery to the purposes of eudiometry, founded 

 on the circumstance already mentioned, that nitrogen gas, as well 

 as several other gases, are absolutely without effect in as far as re- 

 gards any alteration of their volume, and may therefore be ad- 

 vantageously employed in the analysis of atmospheric air, or other 

 mixed gases. Several experiments of this nature are described, and 

 others suggested for future trial. Various theoretical views, arising 

 from this train of inquiry, are then discussed ; particularly with re- 

 ference to the contact theory, with which the author conceives that 

 the action of the gas battery is not reconcileable ; and also to the 

 source of the caloric evolved during voltaic action, which he is 

 strongly inclined to think is in the battery itself. 



2. A paper was also read, entitled " Contributions to Terrestrial 

 Magnetism." No. IV. By Lieut.-Colonel Edward Sabine, R.A., 

 F.R.S.* 



In the present number of these contributions, the author resumes 

 the consideration of Captain Sir Edward Belcher's magnetic obser- 

 vations, of which the first portion, namely, that of the stations on 

 the north-west coast of America and its adjacent islands, was dis- 

 cussed in No. 2. The return to England of H.M.S. Sulphur by 

 the route of the Pacific Ocean, and her detention for some months in 

 the China Seas, have enabled Sir Edward Belcher to add magnetic 

 determinations at thirty-two stations to those at the twenty-nine 

 stations previously recorded. 



The author first describes the experiments which he instituted 

 with the different needles employed by Captain Sir Edward Belcher 

 for determining the coefficient to be employed in the formula for 

 the temperature corrections; and takes this opportunity of noticing 

 the singular fact that, in needles made of a particular species of 

 Russian steel, this coefficient is negative ; that is, in these needles, 

 an increase of temperature increases the magnetic power. M. 

 Adolphe Erman describes this particular kind of steel as consisting 

 of alternate very thin layers of soft iron and of steel, so that when 

 heated the soft iron layers increase their magnetic intensity and the 

 steel layers diminish theirs. 



He next considers the more important question of the steadiness 

 with which the needles may have maintained their magnetic condi- 

 tion. By intercomparison of the results obtained at various stations 

 with the different needles employed, he assigns corrections to be 

 applied to the determination of the magnetic force deduced from 

 the observed times of vibration. The magnetic force thus corrected, 

 from the observations with each of the needles employed at the 

 various stations visited by Sir Edward Belcher, is then given in a 

 general table of results. The observations of the inclination of the 

 needle are given in another table ; and a third table contains the 



[* A notice of No. III. of these Contributions was given in Phil. Mag. 

 S. 3. vol. xx. p. 506; and of No. II. in vol. xviii. p. 549; for No. V. see 

 p. 380.] 



