54 



Mr. G. Cook on the Collapse of 



variation in any particular tube. A greater diameter was 

 undesirable in view of the fact that the length was limited 

 by the testing appliances to about 13 inches. It was found, 

 by means of a micrometer gauge, that the greatest and least 

 diameters did not differ by more than \ per cent., and 

 although a variation of one-thousandth of an inch in the 

 thickness is equivalent to 2 or 3 per cent., it was found that 

 the departure from uniformity rarely exceeded this amount. 

 The manner in which the ends of the tubes were closed 

 before testing is shown in fig. 1. Two cast-iron disks were 



Eff. 1. 



machined with circular slots, against which the inner surface 

 of the tube accurately fitted. Longitudinal stress in the 

 tube was avoided as far as possible by providing a central 

 strut against which the disks were screwed, the joint being- 

 made tight by means of a thin lead washer, a small clearance 

 being left between the ends of the tube and the bottom of 

 the slots. The slots were then filled with lead wool ham- 

 mered in with a caulking tool, and the joint thus made was 

 found to be perfectly tight even against pressures as high as 

 2000 lb. per sq. in. A small hole drilled through one of the 

 disks, and communicating with a tube leading to the 

 atmosphere, ensured that the internal pressure remained 

 atmospheric. 



The enclosure in which the tubes were placed for testing- 

 was a vessel used for various experimental purposes, and 

 designed to withstand an internal pressure of 3000 lb. per 

 sq. in. It was provided with three valves, to one of which 

 was connected a hydraulic force-pump, the other two serving 

 as connexions for pressure-gauges, and as outlets for the 

 air when the vessel was filled with water at the commence- 

 ment of the test. The connexion between. the interior of 

 the tube and the atmosphere consisted of thick copper tubing- 

 passing through one end of the vessel and attached to a 



