; ADDRESS. xls 
that the rate of increase known to us by observation continues further 
down, and is not counterbalanced by a considerable increase in the tempe- 
rature of fusion occasioned by pressure, the present state of the earth would 
be that of a solid crust of eighty or a hundred miles in thickness, enveloping 
a fluid nucleus. Mr. Hopkins considers this state to be inconsistent with the 
observed amount of the precession of the equinoxes, and infers that if the 
temperature of fusion be considerably heightened by pressure, the conclusion 
_ must be unavoidable that the earth is solid at the centre. Mr. Hopkins is 
assisted in these experiments, which are carried on at Manchester, by the 
well-known engineering knowledge of Mr. Fairbairn, and the equally well- 
known experimental skill of Mr. Joule. The principal difficulties attending 
the experiments with substances of low temperatures of fusion have been 
Overcome, and strong hopes are entertained of success with substances of 
more difficult fusibility. ‘The pressures employed are from three to four 
tons to eight and ten tons on the square inch. The latter is probably equal 
to the pressure at several miles beneath the earth’s surface. 
From Heat the transition is easy, and by many may be deemed natural, to 
Terrestrial Magnetism, a science which, more perhaps than any other, has 
profited by the impulse and systematic direction communicated to it by the 
British Association, and which perhaps more than any other required such 
external aid. In the infancy of a science, the phenomena of which present 
on our first acquaintance with them a great appearance of complexity, the 
path by which its progress may be advanced may be by no means easy to 
discern ; and individual explorers inay well, under such circumstances, be 
discouraged by doubts whether their labour will be recompensed by pro- 
portionate success, as well as disheartened by the little sympathy which is 
usually given to investigations which hold out but little immediate prospect 
___ of practical utility. Some there have been however from time to time, who, 
& impressed with a persuasion of the position which magnetism deserves to 
_ take, and which sooner or later they believe it will take, amongst the phy- 
_ sical sciences of the highest order, have not spared this precursive labour, 
and have been uniformly conducted by it fo the same general conclusion, 
viz. that in order to obtain a sufficient foundation of facts upon which to 
) raise a fitting superstructure of inductive reasoning, it would be necessary to 
q organize a system of cooperative research, in which the labours of many 
- might be united agreeably to concerted arrangements ; and that as such re- 
searches would require to be carried on nearly at the same epoch at many 
distant parts of the globe, for which private resources were inadequate, public 
assistance must be sought. That this conclusion was extensively recognised 
. and acquiesced in is sufficiently attested by the readiness so renerally mani- 
_ fested by governments and individuals in all countries where mental cultivation 
is regarded to take part in the general system of magnetic cooperation pro- 
posed by this country in 1838. Inthe years which have since elapsed, the 
energy and zeal of those who have engaged in these researches have accumu- 

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