256 A short Account of Horizontal Water-W heels. 
or broken in the lower part of them, which in my opinion arose 
from the unequal temperature and expansion in the exterior part 
of thie boiler; this unequal temperature is caused by a quantity 
of: water at all times under the flue, and consequently of lower 
temperature than the water above the flue; thereby causing the 
upper part of the boiler to expand ina greater ratio than the 
ander part. of the boiler, which in ‘my opinion caused the frac- 
tures alluded to. This circumstance induced me to make use of 
wrought-iron boilers, as I have explained: or described, ‘in pre- 
ference to the other. a 
In a steam boat, what boiler. would you most récomiidit to 
be used to insure safety to the persons on board; a wrought- 
‘iron or a cast-iron boiler ?—A wrctnee iron boiler, properly con- 
structed. . 
What safety-valves would you recommend to be placed: to 
boilers on board steam-bhoats, to insure the greatest safety, or to 
guard against the boiler’s exploding ; I mean as to number ?—I 
recommend at least two safety-valves ; the one to be placed un- 
der the lock and key of the proprietor of the vessel, so’secured 
as not to be accessible to the engine-man 3 and one which the 
engine-man has the usual control of. 
Have you any thing to recommend with regard to the parti- 
eular construction of these safety-valves, so as to insure their 
acting and constant operation ?—I would recommend the valve 
to be “nearly flat or quite so, which I apprehend would he:less 
liable to be fastened by the difference of temperature to which 
the valve and the seat might occasionally be subjected. 
I suppose such a safety- valve would not be liable to be im- 
peded by much friction?—As little friction as perhaps can be. » 
You have not any thing particularly to suggest ?—No, 
[To be continued. | ) 2 
XUUMI.. A short Account of Horizontal Water- Wheels. By 
W. Apamson*, Esq. if 
Ox perusing the works of mechanical writers, it appears, that 
tmany attempts have been made to construct horizontal water- 
wheels, on such a principle as would give them sufficient power 
for mechanical purposes; but that: these attempts have often 
failed. 
The principal kinds, of which we have any account, are : 
1. Such as have their vanes or floats placed round the rim, 
like those of a wind-mill, and which are made much-broader 
than the vein of water which is to strike them; the water is de- 
* Communicated by the Author. 
; ; livered 
