490 ADDRESS DELIVERED BEFORE THE BRITISH ASSOCIATION 



instruments meteorological and magnetical, as well as astronomi- 

 cal to a high point on the Peak of Teneriffe. His stations were 

 two in number, 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 vain in a 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 intimately connected with Astronomy, and next claim 

 our attention. 



The results of the Ordnance Survey of Britain, so far as they 

 relate to the earth's figure and mean density, have been lately laid 

 before the Royal Society by Colonel James, the Superintendent of 

 the Survey. The ellipticity deduced is -^WW-TS- ^ ne mean spe- 

 cific 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 im- 

 portant accession, in the results of the Tidal Observations made 

 around the Irish coasts in 1851, under the direction of the Eoyal 

 Irish Academy. The discussion of these observations was under- 

 taken 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 Moon in the diurnal tide a problem which 

 was proposed by the Academy, as one of the objects to be attained 

 by the contemplated observations, and which has been now for the 

 first time solved. From the comparison of these effects Professor 

 Haughton has drawn some 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 lumina- 

 ries, but also on the depth of the sea; and this, accordingly, 



