FOR THE ADVANCEMENT OF SCIENCE, 1857. 491 



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 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 is such as to indicate that 

 their wide difference from the former is no't attributable to errors 

 of observation. Professor Haughton throws out the conjecture 

 that the depth, deduced from the tidal intervals and ages, cor- 

 responds to a different part of the ocean from that inferred from 

 the heights. 



The phenomena of Terrestrial Magnetism present many close- 

 analogies with those of the tides ; and their study has been, in a 

 peculiar manner, connected with the labours of this Association. 

 To this Body, and by the hands of its present General Secretary, 

 were presented those Reports on the distribution of the Terrestrial 

 Magnetic Force which re-awakened the attention of the scientific 

 world to the subject. It was in the Committee-rooms of this 

 Association that the first step was taken towards that great 

 magnetic organization which has borne so much fruit; it was 

 here that the philosophical sagacity of Herschel guided its earlier 

 career ; and it was here again that the cultivators of the science 

 assembled, from every part of Europe, to deliberate about its 

 future progress. It was natural, therefore, that the results ob- 

 tained from such beginnings should form a prominent topic in the 

 addresses which have been annually delivered from this Chair; 

 and the same circumstances will plead my excuse, if I now revert 

 to some of them which have been already touched upon by my 

 predecessors. 



It has been long known that the elements of the earth's 

 magnetic force were subject to certain regular and recurring 

 changes, whose periods were, respectively, a day and a year, and 

 which, therefore, were referred to the Sun as their source. To 

 these periodical changes Dr. Lament, of Munich, added another 

 of ten years, the diurnal range of the magnetic declination having 



