to direct experiment, and the Laws of Resistance as far as possible ascertained, and the necessary formula deduced for the future guidance of the practical mechanic and engineer. These objects have, it is believed, been attained by the results developed in the experiments enumerated in the following Tables.

EXPERIMENTS.

Resistance of Tubes to Collapse.

In these experiments the tubes were composed of plates of uniform thickness, and of the form and size shown by the figures in the column of remarks. The form after collapse is also indicated by the woodcuts.

On consulting Table I., it appears that tubes of the same diameter and the same thickness of plates vary in strength when of different lengths. The tubes of 19 inches and those of 40 inches differ widely in their powers of resistance. Comparing the results of Experiments 1 and 2 with those of Experiments 3 and 4, we find that the latter, while of twice the length, bear less than half the pressure. Comparing these with Experiment 5, we find that tube E, 5 feet long or three times as long as A and B, exhibits only about one-third of their mean strength. Similarly, E, which is the length of D, bears only about the pressure.

Tube F, Experiment 6, may be considered as composed of three distinct tubes, each 1 foot 7 inches long. It was made with two perfectly rigid rings, soldered to the outside of the tube to keep it in form and prevent collapse at those points. The result of this alteration was to increase the strength of the tube threefold, as is evident on comparing it with tube E.

Table II. gives indications of the same law of resistance as the last. It will be observed that the tubes

043

22.0

that is, whilst the diameters are to one a the pressures of collapse are as 65: 315, nearly. These comparisons, which might evidently point to a law affecting the diam that of the lengths.

In order to ascertain the different power of tubes composed of thick plates and of meters, a strong tube only 9 inches in formed of a plate 4-inch thick, was constru and compare with another tube, also of 418-inches in diameter. The 9-inch tube 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 4th 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 secondly, to compare with the tube 18 inc

being screwed to the covers of the cylinder, were to some extent in a state of tension, owing to the necessity of having to screw up the air-tube tight in order to prevent leakage. This, with the weakness of the ends of the first two tubes, will account for the discrepancies in the Table. Making allowances on this ground, and taking the mean of the experiments, we arrive at the conclusion that the results approximate closely to the law that the strengths are inversely as the length; and this, it will be observed, is the result arrived at in the comparison of the 4-inch tubes.

Thus the mean strength of the tubes, 30 inches long, experiments G, H, K, L, is 53 lbs. per square inch. Now by the above inverse proportion, we may calculate from this the strength of a tube 59 inches long; thus,

59 30: 52: x=27,

the result being 32 in the above Table, Experiment 9, a difference of 5 lbs. only.

This law receives remarkable confirmation from Experiment 6 on tube F. This tube had, as already explained, two rigid cast-iron rings firmly soldered to it so as to divide its length into three equal parts. The result was to increase the strength threefold, or, in other words, to make it equal in strength to a tube of one-third the length.

The next series of tubes submitted to experiment were 8 inches in diameter, and of the same thickness as the preceding. In these experiments it will be seen that the same law in respect of the length prevails, and is perhaps more strikingly exemplified than in either of the preceding series. Perhaps from their larger size these tubes were less affected by defects of workmanship. Like the last, they had an outlet for the escape of the air, and collapsed with loud reports.