This is a question not easily answered, as we have no experimental facts sufficiently accurate to refer to; and the difference of temperature of the furnace on one side, as compared with that of the water on the other, increases the difficulty, and renders any investigation exceedingly unsatisfactory. Judging, however, from practical experience and observation, I am inclined to think that the strengths of the metals are not much deteriorated. My experiments on the effects of temperature on cast-iron* do not indicate much loss of strength up to a temperature of 600°. Assuming therefore that copper and wrought-iron plates follow the same law, and taking into account the rapid conducting powers of the former, we may reasonably conclude that the resisting powers of the plates and stays of locomotive boilers are not seriously affected by the increased temperature to which they are subject in a regular course of working. This part of the subject is, however, entitled to future consideration; and I trust that some of our able and intelligent superintendents will institute further inquiries into a question which involves considerations of some importance to the public, as well as to the advancement of our knowledge in practical science.

NOTE.

In order to test with accuracy the tensile power of the different descriptions of stays used in locomotive boilers, and to effect a comparison between those screwed into the plates and those both screwed and riveted, it was deemed expedient to repeat Mr. Ramsbottom's experiments on a larger scale; and by extending the tests to copper stays as well as iron ones, it was considered that no doubt could exist as to the ultimate strength of those simply screwed, the tensile powers of the stays themselves, and the relative difference between those and the finished stays when screwed and riveted on both sides of the fire-box.

* Vide the Transactions of the British Association for the Advancement of Science, vol. vi. p. 406.

The large lever and requisite apparatus being at hand, the experiments proceeded as follows:

Experiments to determine the Ultimate Strength of Iron and Copper Stays generally used in uniting the Flat Surfaces of Locomotive Boilers.

EXPERIMENT IV.-Copper stay, aths of an inch in diameter, screwed and riveted into a copper plate 3ths of an inch thick.

It will be observed, on comparing the results obtained from the above experiment, that iron plates and iron stays are considerably stronger than those made of copper. It may not be advisable to have the interior fire-box made of iron, on account

of its inferior conducting powers and its probable durability; but so far as regards strength, it is infinitely superior to that of copper, as may be seen by the following

On the above data, it will be found that the iron stay and copper plate (not riveted) have little more than one-half the strength of those where both are of iron; that iron stays screwed and riveted into iron plates are to iron stays screwed and riveted into copper plates as 1000: 856; and that copper stays screwed and riveted into copper plates of the same dimensions, have only about one half the strength of those where both the stays and plates are of iron. These are facts in connexion with the construction of locomotive, marine, and other descriptions of boilers, having flat surfaces, which may safely be relied upon, and that more particularly when exposed to severe strain, or the elastic force of high-pressure steam.

APPENDIX III.

Boiler Explosion at Rochdale, July 1854.

In accordance with instructions received from the coroner and jury in this case, I visited the scene of the accident on Monday last, and having made a careful inspection of the debris which covers the premises, site of boiler, steam-engine, &c., I have now to report as follows:-With the exception of some parts of the boiler and fragmental parts of the machinery, which had been removed when searching for the bodies of those killed, I found the buildings, steam-engine, boiler, and machinery a heap of ruins. The boiler was torn into eight or ten pieces, one portion (the cylindrical part) flattened and imbedded at a considerable depth in the rubbish, and the two hemispherical ends burst asunder and driven in opposite directions to a distance of 30 to 35 feet from the original seating of the boiler. Other parts of the cylinder and ends were projected over the buildings across Gashouse Lane, and lodged in a field, at a distance of 90 yards from the point of projection. To one of these parts was attached the 2-inch safety-valve, which was torn from the boiler by the force of the explosion, and carried along with its seating over a rising ground to a distance of nearly 250 yards. The other portion of the cylindrical part of the boiler was found on the opposite side in the bed of the river, and the hemispherical end of this part (furthest from the furnace) was rent in two, and thrown on each side to a distance of 30 or 35 feet. These two pieces had evidently come in contact with the chimney, razed it to the ground, and finally lodged themselves in the margin of the river. The 3-inch safetyvalve and pipe attached to that portion of the boiler imbedded in the river was broken from the flange, and with an extended range the 2-inch valve was projected over the river into a meadow at a distance of 150 to 200 yards. Of the steamengine there is not a vestige to be seen, except the fly-wheel, and a pump-rod which lies beside it, covered with bricks. This