— 
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 charaeterized 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. 8. 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 Construction of. opertable 
Mercurial Pendulum, accompanied by Experiments.. The cis- 
tern is made entirely of cast-iron :.the adoption of which metal 
permitted the cistern to be turned perfectly cylindrical within and 
Without, and of thus simplifying the elements of calculation for 
the height of a perfect cylindér of mercury requisite for eompen- 
sating the effects of variable temperature on the rod, an advan- 
taze 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 mereurial 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- 
Vou. XXXV.—No. 2. 37 
