Collapse of Tubes by External Pressure. 



697 



plot different curves for the values 2, 3, .... etc. of k. This 

 thas been done in fig. 3, the following values being assumed 

 for the constants : — 



E = 3 x 10 7 pounds per sq. inch, 

 10 



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From an inspection of these curves we see that long tubes 

 will always tend to collapse into the 2-lobed form, since the 

 curve for k = 2 then gives the least value for the collapsing 

 pressure, but that at a length corresponding to the point A 

 the 3-lobed form of distortion becomes natural to the tube, 

 and for shorter lengths still, of which the point B gives the 



