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Proceedings of the Royal Society 
see, on this theory, how it can be explosively taken in on the 
sudden passage from liquid to vapour. 
Aitken’s experiments tend to show, what J. Thomson only specu- 
latively announced, that possibly vapour may not be condensed (in 
the absence of a nucleus), when compressed iso thermally, even at 
ranges far beyond the maximum of pressure indicated in Thomson’s 
figures. Hence it would appear that the range of instability is much 
less than that given by Thomson’s figures, and may (perhaps) be 
looked on as a vanishing quantity ; the corresponding part of the 
isothermal being a finite line parallel to the axis of pressures, corre- 
sponding to the sudden absorption or giving out of latent heat. 
Monday , 2nd February 1885. 
THOMAS STEVENSON, Esq., Memb. Inst. C.E., President, 
in the Chair. 
The following Communications were read : — 
1. The President delivered the following Address : — 
With the prospect of addressing you for the first time since you 
did me the very great honour of asking me to act as your President, 
I felt somewhat at a loss to determine on what subject I should 
venture to speak to you ; but, at last, I resolved to refer to an 
exceedingly important question of maritime engineering practice, 
which gave rise to very lengthened inquiries before Committees 
during the last two Sessions of Parliament, involving a contem- 
plated expenditure of many millions sterling, and deeply affecting, 
for good or evil, the entrance from the sea to the great port of 
Liverpool. I refer to the proposed Manchester Ship Canal. 
That scheme (for the following remarks have, of course, no 
reference whatever to the scheme as now proposed for sanction by 
Parliament) cannot but be regarded as involving one of the most 
momentous physical questions that ever was raised in Britain, and 
although such a question may, perhaps, never again become one of 
national import in this country, still, I think, no apology is neces- 
sary for bringing it before the notice of this Society. 
About half a century ago a principle was admitted into the prac- 
