ae 
4 ADDRESS. hi 
: 
ahéé of establishing a large reflector at some elevated station in the Southern 
Hemisphere. In the meantime, and to gain (as it were) a sample of the 
resilts which might be expected from a more systematic search, Professor 
Piazzi Smyth undertook, last summer, the task of transporting a large collec- 
tion of instrumentsmieteorological and magnetical, as well as astronomical 
—to a high point on the Peak of Teneriffe. His stations were two in num- 
ber, at the altitudes above the sea of 8840 and 10,700 feet respectively ; and 
the astronomical advantages gained may be inferred from the fact, that the 
heat radiated from the Moon, which has been so often sought for in vainina 
lower region, was distinctly perceptible with the aid of the thermo-multiplier. 
| The researches relative to the Figure of the Earth, and the Tides, are in- 
timately connected with Astronomy, and next claim our attention. 
) The results of the Ordnance Survey of Britain, so far as they relate to the 
Sarth’s figure and mean density, have been lately laid before the Royal So- 
ciety by Colonel James, the Superintendent of the Survey. The ellipticity 
_ deduced is ~~. The mean specific gravity of the Earth, as obtained from 
the attraction of Arthur’s Seat, near Edinburgh, is 5°316,—a result which 
accords satisfactorily with the mean of the results obtained by the torsion 
balance. Of the accuracy of this important work it is sufficient to observe, 
that when the length of each of the measured bases—in Salisbury Plain, and 
on the shores of Lough Foyle—was computed from the other, through the 
-whole series of intermediate triangles, the difference from the measured 
length was only 5 inches in a length of from 5 to 7 miles. 
: Our knowledge of the laws of the Tides has received an important acces- 
sion; in the results of the Tidal Observations made around the Irish coasts 
in 1851, under the direction of the Royal Irish Academy. The discussion of 
_ these observations was undertaken by Professor Haughton, and that portion 
of it which relates to the diurnal tides has been already completed and 
_ published. The most important result of this discussion is the separation of 
_ the effects of the Sun and the Moon in the diurnal tide,—a problem which 
was proposed by the Academy, as one of the objects to be attained by the 
- eontemplated observations, and which has been now for the first timie solved. 
_ From the comparison of these effects Professor Haughton has drawn somié 
_ remarkable conclusions relative to the mean depth of the sea in the Atlantic. 
In the dynamical theory of the tides, the ratio of the solar to the lunar effect 
depends not only on the masses, distances, and periodic times of the two 
luminaries, but also on the depth of the sea; and this, accordingly, may 
_ be computed when the other quantities are known. In this manner Professor 
Haughton has deduced, from the solar and lunar coefficients of the diurnal 
tide, a mean depth of 5-12 miles,—a result which accords in a remarkable 
‘manner with that inferred from the ratio of the semidiurnal coefficients, as 
obtained by Laplace from the Brest observations. The subject, however, is 
far from being exhausted. The depth of the sea, deduced from the solar 
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