48 Difference of Longitude.—Earthquake at Sea. 
17, Toa slave of either sex, for the same, a similar pre- 
mium. 
«“ XII. That the prizes to be bestowed by the society shall 
consist of silver medals of two sizes, and of premiums in money.” 
XXIII. Intellience and Miscellaneous Articles. 
DIFFERENCE OF LONGITUDE BETWEEN GREENWICH AND 
fafRARAS. 
"PoE subjoined is a notice of Mr. Herschel’s paper on this 
subject, read before the Royal Society on the 12th of Ja- 
nuary. po ee set 
“An Account of a Series of Observations to determing 
the Difference of Longitude between the National Observa- 
tories of Greenwich and Paris; by J. F. W. Herschel, Esq. 
Sec. R.S.: communicated by the Board of Longitude.” 
In this paper, after stating the wish expressed by the French 
Ministry of War, that the above determination should be made, 
with the ready accession to their desire of our own Board of 
Longitude, and describing the method resorted to, Mr. Her- 
schel gives the observations in detail. They were made by’ 
himself and one French officer on this side of the Channel, and _ 
by Capt. Sabine and another French officer on the coast of, 
France. Their general result is 9! 21,55" for the difference: of 
longitude between the two Observatories; and though many 
of the observations had been rendered unavailable by un- 
toward circumstances which it was impossible to foresee or to 
obviate, ‘Mr.-H, stated that this determination was not likely. 
to require a correction exceeding 1-10th of a second, and ver 
unlikely to want one of twice that amount,—Anu. of Phil. -. 
- EARTHQUAKE FELP AT SEA; IN FEBRUARY 18265. : 
There are few observations of greater importance, in refer- 
ence to the theory of earthquakes, than the determination. of 
the exact time when they are felt at sea, The place where 
they have their origin,—the velocity with which they are pro- 
pagated,—and their probable depth beneath the surface, may 
be inferred from a series of accurate obseryations.on the effects. 
which they produce, and the. time when they.are felt. at dif- 
ferent points on the earth’s surface. _. oi a 
. The earthquake which was experienced at Lisbon, on the 
2d February 1816, at five minutes past midnight, was felt at 
sea by the Portaguese vessel, the Marquis de Anggja, bound 
from Bengal to Lisbon, at the-distance of 270 leagues rom 
ey ; : at 
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