MR. R. V. SOUTHWELL ON THE GENKKAL THEORY OF ELASTIC STABILITY. 2S8 



It is, however, of interest to compare the general shape of the theoretical curve 

 CBAE (fig. 3) with the results of experiment, and fig. 4 has been constructed for this 

 purpose. It represents a number of tests conducted by the author upon seamless 

 steel tul>e (0'028 inches thick and 1 inch in external di;mn'ter), and shows the relative 

 amounts of resistance to external pressure offered by different lengths of tube. In 

 these experiments (selected for fig. 4 from a more comprehensive series which is still 



Unsupported. 5 Length of 10 Tube in, 15 fnrheg. 20 



Fig. 4. 



in progreas) the ends of the tube were gripped by means of slightly conical plugs and 

 sockets, the interior being kept in free connection with the atmosphere, and no 

 attempt was made to balance the axial thrust due to hydrostatic pressure on the 

 plugged end of the tube. Other experiments have shown that the existence of this 

 thrust is not seriously important. 



It will be seen that the general shape of the theoretical curve is well reproduced, 

 as well as the changes in the number of lobes which characterize the distorted cross- 

 section. Similar results to those of fig. 4 have been obtained by CARMAN,* but his 

 experiments were not sufficiently numerous for a satisfactory comparison with the 

 theoretical curve of fig. 3, his object in conducting them being merely to discover 

 what is the limit of length beyond which the strength of a tube may be taken as 



Of. footnote, p. 210. 



