British Association for the Advancement of Science. 289 



regions, very generally agreeing in position with the centers of 

 maximum magnetic intensities ; and like them, too, the maxi- 

 mum of North America indicated a decidedly higher degree of 

 cold than that which characterized the Siberian pole. Also, that 

 the lines of equal mean temperature, as they surrounded these 

 poles, had such a relation to the lines of equal magnetic intensity, 

 as to point out clearly some yet unknown connexion between 

 these two classes of phenomena. Prof. Bache, of Philadelphia, 

 made some remarks on the importance of connecting the obser- 

 vations making in the U. S. with any which the Association 

 might institute in the British Colonies in North America. Con- 

 siderable progress had, within a few years, been made in Amer- 

 ica in the science of Meteorology. The abstracts of the reports 

 of Meteorological observations from the academies of the State 

 of New York, and the deductions made from them by Sir D. 

 Brewster, had been a great stimulus to increased activity in that 

 department. The recommendations of Sir John Herschel, had 

 not only been adopted by individuals, but had led to the forma- 

 tion of societies for the cultivation of meteorology. He hazarded 

 nothing in promising the hearty concurrence of meteorologists in 

 the United States in any extensive plan which the British Asso- 

 ciation should sanction. 



A paper from Prof. Powell followed, On some points connected 

 with the Theory of Light. 



Mr. Dent then read a paper On the Constrnctiori of a portable 

 Mercurial Pendulutn., accoinpanied by Experiments. The cis- 

 tern is made entirely of cast-iron : the adoption of which metal 

 permitted the cistern to be turned perfectly cy iindricai within and 

 without, and of thus simplifying the elements of calculation for 

 the height of a perfect cylinder of mercury requisite for compen- 

 sating the effects of variable temperature on the rod, an advan- 

 tage which glass did not allow. The homogeneity of the ma- 

 terial also facilitates the reductions for temperature, by equalizing 

 this throughout, and also permits the bearings to be diminished 

 in number, and simplified in construction, when compared with 

 the usual mercurial pendulum having glass cisterns. The sus- 

 pending rod passes through a hollow screw, and is secured by a 

 pin going through both. The hollow screw passes through the 

 axis of the cistern, and the cistern is constructed to move round 

 this screw, which admits of shortening or lengthening the pen- 



VoL. XXXY.— No. 2. 37 



