MK. (4. T. TAYLOR ON TIDAL FRICTION IN THE IRISH SEA. 
5 
is not sufficiently great to give rise to much difference between the square root of the 
mean square of the velocity and the mean velocity, or between this and the cube root 
of the mean cube of the velocity. By taking V = 2|-knots =114 cm. per second 
in (8) we slightly under-estimate the friction ; we shall not in any case over-estimate it. 
Using in (8) the value K = 0’002,'^' and remembering that p, the density of sea¬ 
water, is I'03, it will be found that /r, the mean rate of dissipation of energy, per 
square centimetre per second, in the Irish Sea at spring tides is 
iv = 
0-002 (1-03) (114)® 
1300 ergs per square centimetre per .second. (9) 
Using the least admissible value of Kt it will be found that 
u' = 1040 ergs per square centimetre per second. (lO) 
Mr. Street’s estimate, when reduced to C.G.S. units, is 7 ergs per square 
centimetre per second, which is only of our minimum estimate.^ 
Rate at which Energy enters the Irish Sea owing to the Action of External Forces. 
The amount of dissipation found by the method just described is so different from 
that obtained by Mr. Street, and so much larger than any previous estimate of 
tidal friction that I have come across, that it seemed worth wirile to try and verify 
it, if possible, by some different method. Instead of trying to measure the rate of 
dissipation at every point of the Irish Sea, I have calculated the rate at which energy 
enters the Irish Sea through tlie North and South Channels. To this must be added 
the rate at which work is done by lunar attraction on the waters of the Irish Sea. 
The sum of these will give the rate at which the energy of that sea is increasing,.' 
lAns the rate of dissipation of energy. When tlie average values of these expressions 
are taken during a complete tidal period it is evident that, since the energy of the 
Irish Sea does not increase or decrease continually, the average value of the rate of 
increase in energy is zero. Hence the average rate of dissipation of energy by the 
tidal currents can be found. 
Rate at tvhich Energy flows into the Irish Sea. —The calculation of the rate at 
which energy flows into the Irish Sea is very simple. Consider the flow of energy 
across the surface, S (fig. l), formed by the vertical lines between a closed curve, -s-. 
on the surface of the sea and its projection on the bottom. 
* See equation (7). 
t See equation (4). 
I Mr. Street informs me that since publishing the paper already referred to, he has obtained other 
results which confirm his previous results. He hopes to publish them when circnmistances permit. 
