510 REPORT—1868, 
From tide-observations made at considerable intervals, and reduced in the 
manner followed above, some approximation to the secular changes (caused 
by the widening or narrowing, the deepening or filling up of rivers) can to 
some extent be estimated, and embankments or other protections carried 
out at those places where the tide is making encroachments, and a surer 
foundation afforded for the reclamation of land. 
There can be no doubt that in all these operations every advance towards 
more perfect knowledge of the tidal movements will be accompanied by an 
economy of time and labour which in the aggregate must be very considerable. 
40. It may here be mentioned that there now appears to be a considerable 
difference in the spring-range of the tide in the Thames at the London Docks 
(amounting to 13 inches in twenty-five years), caused, it is supposed, by the 
remoyal of obstructions, extensive dredging, and the construction of the em- 
bankment. In the Admiralty Tide-tables the heights of high water have 
been augmented by the apportioned amount, but no correction has been applied 
to the times of high water, which are also probably different. 
It is to be hoped that the Lords Commissioners of the Admiralty may be 
pleased to direct that new determinations of the tides in the Thames and 
other places be made with a view of obtaining the requisite foundation for 
more extensive tide-tables than those now published, and supplying to the 
mariner more accurate and complete knowledge of the tides along our coasts. 
Report of the Committee for the purpose of investigating the rate of 
Increase of Underground Temperature downwards in various Loca- 
lities, of Dry Land and under Water. Drawn up by Professor 
Everert, at the request of the Committee, consisting of Sir W1LL1aM 
Tuomson, LL.D., F.R.S., Mr. E. W. Briyney, F.R.8., F.G.S., 
Principal Forsus, LL.D., F.R.S., Mr. Ancurpatp Guixie, F.R.S., 
F.G.8., Mr. James Guaisuer, F.R.S., Rev. Dr. Granam, Mr. 
Freemine Jenkin, C.L., F.R.S., Sir Coartus Lyewz, Bart., LL.D., 
F.R.S., My. J. Cterx Maxwettz, Mr. Guorcz Maw, F.L.S., F.G.S., 
Prof. Puituirs, LL.D., F.R.S., Mr. Punertiy, F.R.S., F.G.S., 
Professor Ramsay, F.R.S., F.G.S., Mr. Batrour Srewart, LL.D., 
F.R.S., Mr. G. J. Symons, Professor James Toomson, C.E., Pro- 
fessor Younc, M.D., F.R.S.E., and Professor Everert, D.C.L., 
F.RS.E., Secretary. 
Tue following Circular, issued to the Committee in November 1867, explains 
the plan of procedure proposed, and the progress made in the investigation 
up to that time :— 
Srr,—No Meeting of the Committee has yet been held ; and as the Members 
are scattered over the country, it appears undesirable to wait for a Meeting. 
I therefore take this opportunity of laying before vou the suggestions of Sir 
W. Thomson and myself with regard to the system of observation which 
should be adopted, and shall be glad to receive any suggestions of your own 
in reply. 
The object of investigation is the rate at which, in various localities, the 
temperature of the earth increases in going downwards, at depths sufficiently 
great to render the annual range of temperature insensible. 
