34 MR. DARWIN ON THE BODILY TIDES OP VISCOUS AND SEMI-ELASTIC 
Ramsgate. 
Liverpool. 
Hartlepool. 
R' -120 
v +88°-29 
■295 
— 9°-3 
•117 
—31°-2 
■076 ' 
— 1U7 C T 
T14 
+ 160°-6 
Y57 
| +10°-34 
T60 
+ 42°-34 
•220 
—21°-38 
Brest. 
Kurrachee. 
R' -304 
r, —99°35 
•243 
-24°-60 
•410 
-26°-09 
•224 
-76°-78 
We will consider R/ first. 
From these twelve values we find R' = ‘203, with a probable error ;L'0G8. 
The value of IT is almost exactly that indicated by theory (viz., ’207), but the very 
large probable error renders the result so uncertain, that it can only be asserted that 
the results do not disprove a diminution of fortnightly tide. 
With regard to phase, it will be observed that there are eight cases of accelerated 
tide to four of retarded. Two of the retarded tides refer to Hartlepool, and concerning 
this station Sir W. Thomson says in the report: “ There is scarcely sufficient agree¬ 
ment between the results deduced from the long-period tides to be satisfactory, 
although the quantities of some are within reasonable limits.” 
It maybe remarked, in passing, that Cat Island gives a retarded tide, and Toulon an 
accelerated one. 
If. we treat these alterations of phase in the same way as PT was treated, we find a 
mean acceleration of phase of 7°‘85, but with a p.e. several times larger than the 
result itself. But, in fact, with so few and such irregular observations the method 
of least squares is useless. 
The cases of retarded phase certainly show considerably more irregularity than 
those of accelerated phase. If we take the mean of the cases with accelerated phase, 
we shall find an acceleration of 48°, which corresponds in time to an acceleration 
of 1 day 20 hours. 
Now three out of four years of observations show an accelerated tide at Liverpool; 
all three years show an acceleration at Kurrachee ; the Hartlepool observations are 
not of very much value ; while the single year of acceleration at Brest may be set off 
against the single year of retardation at Ramsgate. If then we ask ourselves whether 
acceleration or retardation is the more probable, I think it must be answered in favour 
of acceleration ; and if so there seem to be some indications of a viscous yielding of 
the earth’s mass. It must be admitted, however, that the evidence is exceedingly 
uncertain. 
It does not seem to be noticed in the tidal reports, that amongst the “ Helmholtz 
compound shallow-water tides ” there will be found several which have the same 
period, or very nearly the same period, as the true fortnightly declinations! tide. If 
