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se tubes do not at first etory results. The first, G f 150 lbs. on the square i nuch as to cause its rem me of the rivets which ary repairs, it was again s it gave way with a fore it had been injured br aring it with the mean nts, we find that it shoul it evidently failed at t

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i was a steel tube, of th d divisions to those of the inch lbs. on the

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the middle division. nilar plates of iron, 14 5s. This collapsed with square inch; and th experiments, as will be

33, it would appest han the iron; but we al conclusions from s

drical tube X, which are of the same le ness of plates, and only about half a squa in sectional area, we have for the collaps the former 127.5 lbs., and for that of the where it will be observed there is a loss the strength, in consequence solely of t the tube Bb, or in other words, a cylin support nearly three times the pressur collapse an elliptical tube of the sam proportioned like tube Bb. A simila observable in tube Aa, when compared The change of form, from the cylinder where the diameter was reduced to 12 inc tion and extended as much in another, red powers one-half. The comparative resul the experiments on the thick tube are diff on the thin one, the loss being much grea than in the latter case, although the ratio is about the same. Allowance must, ho for inaccuracies of construction, though v ably have expected a nearer approximati of the deficiency of strength. From t ever, it is obvious that in every construct have to sustain a uniform external pressur is the only form to be relied upon, and from it is attended with danger.

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cylinder covers; they were simply placed in the cylinder, and water pumped in, in the usual manner, until they collapsed as given in Table VII. :—

In the above experiments the tubes do not appear to follow precisely the law of "inversely as the length." Had they done so, the tube BB should not have yielded with a less pressure than 44 lbs. on the square inch. It is, however, impossible to manufacture these tubes truly cylindrical, and hence it follows that slight variations may very materially affect the ultimate strength of the tube.

From three experiments on 4-inch tubes, we derive data more in accordance with the law, as will be seen in Table VIII.

In the above experiments, the second on tube DD is lost, in consequence of the ends being fractured and the water obtaining admission, so as to cause a counteracting pressure in the interior. Experiment 29 agrees closely with the law when compared with 27, its strength being correctly double that of the latter. The 15-inch, although not four times the strength of the 60-inch, exhibits high resisting powers. It is probably difficult to reconcile these discrepancies; but we have in these experiments sufficient data to show that these tubes also follow, in their resistance to collapse, some function of the length; and it is important to observe, that we cannot in practice introduce long tubes into constructions exposed to external pressure, without making very considerable allowance for their loss of strength.

In the earlier experiments the tubes were made of thin wrought-iron plates; but conceiving that it would be of interest to examine how far the laws, which were found to prevail with them, applied also to tubes of other materials, three tubes were made of the following dimensions:

GG. Iron flue, 15 inches in diameter:

-21f

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Plates 125 inch thick.

Web (a a) 25 inch thick.

Rivets inch, at 14 inch apart.

HH. Steel flue, diameters 15 and 15 inches:

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Plates 125 inch thick.

Web (bb) 25 inch thick.

Rivets inch, at 11 inch apart.

JJ. Iron flue, with overlap joints; diameters 14 and

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