Mr. W. Fairbairn on the Resistance of Tubes to Collapse. 535 



drical tube, placed in tbe position of an internal flue, is equally 

 strong in every part when subjected to uniform external pressure ; 

 the length not affecting the strength of a flue so placed. This rule 

 is, however, only true when applied to tubes of infinitely great length, 

 and it is very far from true when the length of the tube does not ex- 

 ceed certain limits, and when the ends are retained in form by being 

 riveted to the boiler, and thus prevented from yielding to external 

 pressure. These facts were fully demonstrated by the experiments 

 related in the Paper, which, for obvious reasons were conducted under 

 circumstances as nearly as possible analogous to those now in actual 

 operation upon a larger scale. With this view, a large and powerful 

 cylinder, 8 feet long, and 2 feet in diameter, was prepared for the 

 reception of the tubes ; and being acted upon by hydraulic pressure, 

 collapse was produced, and the results recorded, as fully explained 

 in the Paper. It will suffice here to state the more important conclu- 

 sions derived from the investigation, which fell under the following 

 heads : viz. — 1st, the strength of tubes as affected by length ; 2nd, 

 the strength of tubes as affected by diameter ; lastly, the strength of 

 tubes as affected by thickness of metal. 



1 . On the first head, the strength as affected by length, the results 

 are conclusive and interesting. Within the limits of from 1 foot 6 

 inches to about 10 feet in length, it is found that the strength of 

 tubes similar in every other respect, and supported at the ends by 

 rigid rings, varies inversely as the length, as may be seen from the 

 following results obtained with 4-inch tubes. 



Resistance of 4-inch tubes to collapse. 



The remarkable differences in the resisting pressure of the above 

 similar tubes will be at once apparent, and it will be found by calcu- 

 lation that they follow the law of inverse proportion, the same as 

 those of larger dimensions, the strengths diminishing as the lengths 

 are increased. 



The same law of resistance is maintained in 6-inch tubes, giving, 

 for a tube 30 inches long, .Oj lbs., and for one 59 inches long only 

 32 lbs. on the square inch, as the pressure of collapse. Again, in 8- 

 inch tubes wc have, in a long gcries of experiments, 32 lbs. per square 

 inch in a tube 39 inches long, and 39 lbs. in one 30 inches long. In 

 the same manner all the experiments on tubes of 10 and 12, and up 

 to 18 inches in diameter may be compared, and the law of resistance is 

 in like manner shown to hold true in every case. Discrepancies to 

 a certain extent do certainly occur ; but they are comi)aratively small, 

 and, as they a[)pear to follow no law, arc evidently to be accounted 

 for from defects in the construction of the tubes inseparable from 

 such a mode of research. 



