of Edinburgh, Session 1884-85. 91 
in twelve hours, making a total scouring power of 742,000,000 
yards. 
Compare this with the resulting loss, and we find that not one- 
twentieth , which Mr Walker feared to authorise at the Tay — not 
one-tenth , as has actually taken place at the Lune — but one-half of 
the whole scouring power would be excluded from the estuary of the 
Mersey. 
With such a result as this, I cannot for a moment doubt that the 
promoters of the Manchester Canal, and Mr E. Leader Williams, 
their engineer, before going to Parliament for the present Bill, 
exercised a wise discretion in resolving to adopt the suggestion of 
Mr Lyster of Liverpool to keep the new Ship Canal — i.e., the one 
now before Parliament — altogether outside of, and therefore clear 
of the land-locked estuary of the Mersey, so as no longer to ex- 
pose the works to the rapid tides and land floods, as in the first 
scheme. 
The lesson, then, as it seems to me, which is to be derived from 
all that has been said, is simply that where there is a conjunction 
of an extensive land-locked estuary, with all, or with many of 
those conditions favourable to silting which I have defined, such a 
state of matters should in all cases be regarded as more or less 
dangerous, and especially so in any river where the depth is already 
reduced by the existence of a shallow bar lying beyond the mouth 
of the river, and exposed to a heavy breaking sea, from the action 
of which it cannot be protected by breakwaters. 
2. On Evaporation and Condensation. By Professor Tait. 
(Abstract.) 
While I was communicating my Note on the Necessity for a 
Condensation Nucleus at the last meeting of the Society, an idea 
occurred to me which germinated (on my way home) to such an 
extent that I sent it off by letter to Professor J. Thomson that 
same night. 
J. Thomson’s idea, which I had been discussing, was to preserve, 
if possible, physical (as well as geometrical) continuity in the 
isothermal of the liquid- vapour state, by keeping the whole mass 
