190 ANNUAL OF SCIENTIFIC DISCOVERY. 



FIGURE OF THE EARTH AND THE TIDES. 



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

 to the earth's figure and mean density, have been lately laid before the Roy.il 

 Society by Col. James, the Superintendent of the Survey. The ellipticity 

 deduced is ^"9 tj--^. The mean specific gravity of the earth, as obtained 

 from the attraction of Arthur's Seat, near Edinburgh, is 5 '3 1 6 ; a result 

 which accords satisfactorily with the mean of the results obtained by the 

 torson 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 Poyle) was computed from the other, 

 through the whole series of intermediate triangles, the difference from the 

 measured length was only five inches in a length of from five to seven miles. 

 Our knowledge of the laws of the Tides has received an important accession 

 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 duscussion, 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 accomplished. 



Prom 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 luminaries, hut 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 co-efficients of the 

 diurnal tide a mean depth of 5' 12 miles a result which accords in a re- 

 markable manner with that inferred from the ratio of the semi-diurnal co- 

 efficients, as obtained by Laplace from the Best observations. The subject, 

 however, is far from being exhausted. The depth of the sea, deduced from 

 the solar and lunar tidal intervals, and from the age of the lunar diurnal tide, 

 is somewhat more than double of the foregoing ; and the consistency of the 

 individual results in such as to indicate that their wide difference from the 

 former is not attributable to errors of observation* Professor Haughton 

 throws out the conjecture that the depth, deduced from the tidal intervals and 

 arjes, corresponds to a different part of the ocean from that inferred from the 

 heights. Address of the President British Association, 1857. 



SECULAR YAHIATIONS IN LUNAR AND TERRESTRIAL MOTION FROM 

 THE INFLUENCE OF TIDAL ACTION. 







The following paper by Mr. D. Vaughan of Cincinnati, was read before 

 the British Association for 1857. 

 Laplace concludes from his elaborate investigations, that the rotation of 



