216 REPORT—1857. 
affecting the strength of a Hue placed in such circumstances. This rule is, 
however, applicable only to tubes of infinitely great length, or to tubes 
unsupported by rigid rings at the extremities; it is very far from true 
where the length of the tube does not exceed certain limits, and where the 
ends are retained in a cylindrical form by being securely fastened in rigid 
frames to prevent their yielding to external pressure. Some experiments 
upon large boilers, with flues 20 to 30 feet long and about 3 feet diameter, 
first led to misgivings on this subject, by indicating the greater strength of 
the shorter flue. This anomalous result induced further inquiry, which not 
proving satisfactory, it was determined to submit the question to experiment, 
in order to prove how far these doubts were entitled to credit 
To attain the objects of the experiments in a satisfactory manner, it was 
necessary that the apparatus for conducting them should be of great strength 
and large dimensions. For this purpose a cast-iron cylinder C, 8 feet long, 
28 inches in diameter, and 2 inches thick of metal, was prepared for the 
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reception of the tubes to be experimented upon. A small pipe, a, was 
connected with a force pump, and by means of this, water was injected into 
the cylinder and the requisite pressure obtained. A second pipe, 6, com- 
municated with two steam pressure gauges, by which the force required for 
collapse was registered ; and the indications of these were checked by a small 
and accurately fitted safety valve d. The large cylinder was fitted at top 
