On comparing the above results, it will be found that there is a near approximation to the strengths being inversely as the lengths. Taking the strength of the first tube, 30 inches long, and calculating the force necessary to collapse the 39 and 40-inch tubes, we have, by calculation,

39: 30:39:x=30 and 40: 30:: 39 : x=29.25;

the difference from the result in the Tables being 2 lbs. in the one case and 13 lb. in the other.

The following results on 10-inch tubes are also remarkably consistent with the above law.

Both tubes gave way, as in the preceding experiments, with a loud report. Comparing them, we have 50:30:: 33:19.8; and by experiment (16) we have 19 lbs.

Equally strong evidence in confirmation of the law respecting the lengths, will be found in the Table of 12-inch tubes. The increase of diameter, without any change in the thickness of metal, does not affect it. On the contrary, this principle of resistance, in the case of tubes with unyielding ends and open for the escape of the contained air, holds true, uniformly, throughout the whole of the experiments on 4, 6, 8, 10, and 12-inch tubes, as nearly as could be expected when due allowance is made. for variations in the rigidity and thickness of the plates, imperfections in the workmanship, and difference in the tension of the sides.

Taking Experiment 20 as correct, we have for the collapsing pressure of a similar tube, 5 feet long, 60:30:: 22:x=11, or 1.5 lb. less than Experiment 19. Similarly, 58: 30::22:x=11·2, or 0.2 lb. more than in Experiment 18. From these results we may reasonably conclude that the law affecting the strength of tubes is, other things being the same, that the collapsing pressure varies inversely as the length.

The tube S, when compared with the 6-inch tubes only one-half the length, required a pressure of less than onefourth to cause collapse. This apparently low pressure, though at first sight anomalous, is confirmed by the result of Experiment 19. Similarly, comparing tubes C and D, Table I., with tubes O and P, Table III., we have, Length. Diameter. Pressure.

that is, whilst the diameters are to one another as 1: 2, the pressures of collapse are as 65: 31.5, or as 2:1 very nearly. These comparisons, which might be continued, evidently point to a law affecting the diameters similar to that of the lengths.

Fig. 2.

In order to ascertain the different powers of resistance. of tubes composed of thick plates and of different diameters, a strong tube only 9 inches in diameter, and formed of a plate 4-inch thick, was constructed, to match and compare with another tube, also of 4-inch plate, and 183-inches in diameter. The 9-inch tube was, however, found to be too strong for the retaining powers of the cylinder, which it would not have been safe to have trusted above 500 lbs. per square inch. Finding the strength of the small tube too great for the containing vessel, two new tubes were made, one with a lapjoint as at A in the annexed sketch, and another with a butt-joint as at B. These tubes were made of plates 1th of an inch thick, the object of the difference being two-fold;—first, to ascertain to what extent the strength of the tube was reduced by the lap-joint; and

B

secondly, to compare with the tube 183 inches in diameter,

o yield very satisfactory results. The first, GG,
y with a pressure of 150 lbs. on the square inch,
began to leak so much as to cause its removal
vessel, to replace some of the rivets which were
t. After the necessary repairs, it was again sub-
experiment, when it gave way with a force of
showing how much it had been injured by the
pressure. On comparing it with the mean re-
all the other experiments, we find that it should
rne about 300 lbs.: it evidently failed at the
nd cannot be relied upon.

the former 127 there it will b the strength, i the tube Bb, pport nearl collapse an e proportioned observable in

ext experimented upon was a steel tube, of the
m and with similar rigid divisions to those of the
. This sustained 220 lbs. on the square inch,
bulged in or collapsed in the middle division.
ast was a plain tube of similar plates of iron, 145
a diameter, but without ribs. This collapsed with
are of 125 lbs. on the square inch; and this
early with the preceding experiments, as will be

The change

where the dis tion and exte

aring Experiments 32 and 33, it would appear steel tube is not stronger than the iron; but we warranted in drawing general conclusions from a xperiment.

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the experim on the thin

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have to su
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