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be taken. With respect to the ventilating fan, at the high 
speed at which it was intended to work, he thought some 
slight gearing might be necessary. 
Mr. Nasmyth now proceeded with his last communication, 
which, like its predecessor, was illustrated by diagrams. 
DESCRIPTION OF AN IMPROVED SAFETY VALVE FOR STEAM 
BOILERS. BY JAMES NASMYTH, ESQ. 
Mr. Nasmyth gave a description of an improved safety 
valve for steam boilers, and referred to the calamitous 
boiler explosions which had been so frequent of late, and 
observed that, as a means of prevention, none was more 
efficient than a good safety valve. He proceeded to in- 
quire what were the causes of the failure of the ordinary 
safety valve — wherein was it deficient? The function of 
a safety valve was to have some part of the boiler which 
would open and allow the steam to escape on a certain 
pressure being reached. This object was very simply 
attained by a valve of the ordinary construction, loaded 
either by a weight attached directly to the valve, or by a 
small weight increased in its efficiency by a system of levers. 
The ordinary safety valve (of which a model was shown) 
was liable to stick fast, owing to the muddy sediment of 
the water collecting round the spindle of the valve. In the 
common construction of valves the conical form was generally 
adopted. It was thus important that the internal and 
external cones should exactly coincide, and it was necessary 
to guide the spindle very correctly into the centre. This 
arrangement was subject to the inconvenience of the spindle 
sticking fast on the one hand, or if it were too slack, it 
would fail to perform its functions. It was highly probable 
that many accidents had arisen from the safety valve not 
having acted efficiently. His improved safety valve consisted 
in doing away with the spindle altogether, and employing the 
