ON THE CONSTRUCTION 



HOOPED CANNON. 



55 



figures) shows a true copy of the lines made upon the register-plate. By this 

 it will be observed that the permanent elongation commenced at a strain of 

 100 pounds, and increased rapidly, at each successive increase of weight, until it 

 reached a length of 101 inches, or the 



Now, on 



o 



comparing 



iVVth part of the length of the wire. 



the results shown in all these figures, we see that those 



periments demonstrate with some degree of precision several physical facts, all 



f 



are 



of high impor 



the 



of cannon upon the prin 



ciple pointed out in the Memoir to which this is a sequel. These facts are 



F 



That with a piece of iron hardened by compr 



and tension, in 



far smaller 



the condition of hard wire, the amount of permanent elongation is 

 than the permanent elasticity up to near the breaking-point, and also that the 

 permanent elongation does not begin until about one-half of the breaking strain 

 is applied. 



Second, That the part of 



elongation, or 



hich is within the elastic 



pow 



of the 



wire, increases verv regularly under equal increments of strain ; 



very 



thus exhibiting the truth of 

 strain. But the 



maxim, Ut 



VlH 



As 



stretch, so the 



permanent elongations made by the same 



enients of 



especially when near the breaking of the wire, are entirely at variance 



this 



th 



maxim 



This will be seen in Figure 4, wher 



ement of 20 pound 



to an existing strain of 120 pounds, produces a permanent stretch of y^ths of 



inch 



of 



while the same increment of 20 pounds, when the wire was 

 280 pounds, increased the length, permanently, full 1J inches 



iler a strain 



d, That, when the material has been subjected to a strain of a given 



amount (say 440 pounds, as in Fig 



the repeated applic 



of 



strain 



within that amount produces no further permanent 



elongation. 



Fourth, That th 



ubjectin 



of the same material to a heat sufficient to burn 



oil 



in contact with it (supposed in this case 



to be 800° Far., at least), will not 



impair 



ticity 



Fifth, That, 

 comparatively 

 elasticity of t 

 body, of a hoop that 



on 



d, the permanent elongation commences 



and that its extent 



which 



inappropri 



been heated to an 



ery large in 



ite is the n 

 jaling temp 



proportion to the 

 upon a cast-iron 



ture ; as it must 



upon 



be loosened, or suffer the cast-iron to break within its grasp, before a strain 

 up to half its tensile strength shall be reached. 

 Guided by the conclusions derived from the preceding experiments, I will 



proceed to compare, with such precision 



as 



the knowledge thus opened to me 



