Tom. Then, when a boiler grows old and thin, if the pressure is very great, it bursts in the weakest part?
Mr. W. Just so; and ingenious men have made some portion of the boiler of a weaker metal—so that, if it burst from the pressure of the steam, it should hurt no one.
Amelia. I cannot understand what you mean.
Mr. W. You see this kettle on the fire:—if we cork up the spout, and fasten the lid down, and let it boil, it will, probably, blow the cork out, and hit some of you; but if, at the back part of the kettle that touches the chimney, we have a part of it made of lead, or tin, it will explode there.
Amelia. Oh! I see now.
Tom. But, father, this cannot account for the tremendous explosions, by which the boiler itself is thrown a great distance, and even factories are blown down.
Mr. W. I think not. I will try to make you understand this, to-morrow.
