236 



Messrs. Sidgreaves and Stewart on Curves of the [Jan. 21 > 



The more salient points of these results are pointed out, such as the 

 preeminently small resistance of water and of bodies containing a large 

 proportion of the elements of water (potential water); the possible connexion 

 of this fact with the results of Magnus concerning the conductivity of 

 hydrogen ; the increased resistance accompanying increased molecular 

 complexity in the case of isotypic liquids, as exemplified by the alcohols 

 and their derivatives : the great resistance shown by the liquids containing 

 halogens. The results obtained by Tyndall in regard to relative diather- 

 mancy are shown to be in accord with the author's results concerning 

 resistance. A highly diathermanous liquid invariably offers great resist- 

 ance to conducted heat. The relation between electrical and thermal 

 resistance in the case of liquids is also briefly discussed. 



II. " Results of a preliminary Comparison of certain Curves of the 

 Kew and Stonyhurst Declination Magnetographs." By the Rev. 

 W. Sidgreaves and Balfour Stewart, LL.D., F.R.S. Re- 

 ceived October 28, 1868. 



The observatories of Kew and Stonyhurst are not far apart, both being 

 in England; the first in the county of Surrey (Lat. 51° 28' 6" N., 

 Long. 0° 18' 47" W.), and the second in the county of Lancashire (Lat. 

 53° 50' 40" N., Long. 2° 28' 10"-2 W.). 



If we bear in mind (as a fact w T ell proved, chiefly by the researches of 

 General Sabine) that magnetic disturbances are of a cosmical nature, we 

 cannot evidently expect any considerable difference between these two 

 stations, and it might be very naturally supposed that the magnetic varia- 

 tions should be precisely the same in each. 



This is no doubt approximately true, but nevertheless there is on cer- 

 tain occasions a residual difference between the indications of the two places, 

 and one which is caught by the eye from the automatic records with very 

 great ease, inasmuch as the instrumental time-scale of these is precisely the 

 same for both places ; and not only is the time-scale the same, but for slow 

 disturbances the vertical spaces traversed by the traces are the same for 

 both declination magnetographs. 



We venture to bring before the Royal Society certain results of an inter- 

 comparison of the declination curves of these two observatories, although 

 only of a preliminary nature, because the subject is one of much interest, 

 and because these results appear to exhibit, superposed upon a disturbance 

 which is mainly cosmical, a comparatively small effect, which appears to 

 be more of a local nature, but which is not unworthy of investigation. 



The records which we have investigated are represented graphically in 

 Plates III. and IV. ; and in them the disturbances which have been 

 measured are denoted by figures attached to their extremities. 



The following Table exhibits the results of these measurements : — 



