15 
as to cause the smoke to pass oS" with some difficulty. 
Having about 18 years ago built one 110 feet high with its 
internal flue wider at the top than at the bottom, it was 
found in practice to answer so well that on applying 14 
puddling and other furnaces to it ; the draft up to that point 
seemed rather to be improved with each additional furnace 
than impeded. I now find the practice becoming a general 
one in Scotland and Lancasliire, which I attribute to my 
having mentioned the circumstance from time to time to 
my friends ; and I do not hesitate to say that in good 
situations 80 feet will be found an ample height for the 
largest engines, and 100 feet in situations less favourable. 
The Chairman having invited discussion — 
Mr. J. G. Marshall said the meeting was much indebted 
to Mr. Hartop for his observations respecting steam boilers. 
One part of the subject which he had explained he thought 
exceedingly satisfactory ; he alluded to his description 
of the superiority of the Cornish boiler, over those com- 
monly used called the waggon boiler. He himself thought 
them much superior, and cliiefly for the reasons that Mr. 
Hartop had stated — their greater adaptation to the applica- 
tion of heat. He had been so far convinced of that that he 
had caused to be erected boilers of that shape ; but there 
was one point which Mr. Hartop had reckoned amongst the 
advantages of the Cornish boiler that he should be rather 
disposed to doubt, and that was its greater safety. The 
external shape of that boiler was undoubtedly stronger, but 
he thought that the internal surface, which had to resist the 
fire, was weaker, by reason of its form, than the ordinary 
boiler ; and he believed that several steam-boat accidents had 
been attributed to the internal shape of the boiler. Its con- 
struction was such that if the internal tube in any degree got 
out of its correct shape it immediately collapsed. Several acci- 
dents had occurred to the Cornish boiler,and he thought it was 
most probably to be attributed to that source. He thought 
it would be desirable as a means of guarding against acci- 
dents, that the makers of those engines should state the force 
they would bear externally and internally ; and it might 
also be of advantage if means were devised for "staying'* 
them. With respect to what Mr. Hartop had said about 
the inutility of extending the length of the boiler, he should 
be disposed to differ from him, inasmuch as the parts which 
received the application of the fire were extended, as well as 
those that did not receive it. With respect to the per- 
formances of the Cornish boilers he also thought that there 
was still a great deal of doubt. The results of experiments 
upon diflferent boilers varied materially, and he thought it 
very possible that they might have been incorrectly taken. 
