102 
At the meeting of the Society on the 1 1th of January last, the 
President drew the attention of members present to certain 
phenomena of this kind, stating that near the angle-iron 
adjoining the smoke-box, the body of a boiler is often found 
deeply grooved or channelled all round the lower part, from 
near the surface of the water on one side to the same height 
on the other, — thus causing a weakening of the plates in 
that part of the boiler, which results in its explosion, when 
in other parts it is very little worn. It M'as asserted that 
stationary boilers are not affected in this way. 
The Author had only the facts to go upon that were 
adduced on the occasion just mentioned, his explanation 
might not therefore be so put as to meet all the varieties of 
cases that may have occurred. The explanation was not so 
much a hypothetical one, as an attempt to trace to their con- 
sequences certain physical forces which must be brought into 
action in the working of a locomotive boiler. These forces 
are (1) chemical, exhibited in the oxidation of the plates, 
which of course would, in a quiescent state of the boiler, act 
uniformly over the greater part of its surface ; (2) mechanical, 
or rather, dynamical, arising from the momentum acquired by 
the water, when the train is proceeding at a high velocity, 
acting, when the train is stopped by the break, with great 
pressure on the forward or smoke-box end of the boiler. This 
dynamical force or pressure, it was argued, besides exerting a 
great strain on the forward end of the boiler, must urge the 
water into oscillatory currents in the neighbourhood of the 
smoke-box, and thus rub off the coating of oxide which had 
formed in any angular recesses where a current could act with 
greatest intensity. This rubbing or eroding process must be 
greatly increased if the water contains sediment of a gritty 
nature. It was thought that the cases of grooving in the 
fragments of boiler-plates, exhibited on the 11th of January, 
might be fairly accounted for by the causes here mentioned. 
Other cases, not being known, could not be discussed. 
