Prof. Challis on Hydrodynamics. 

 Table VIII. 



207 



Bar of 



M. 



B. 



Iron "* 



10 

 12 

 13 

 14 



16 

 24 



26 



28 



Soft steel 



Medium hard steel 



Hard steel 





On the basis of the preceding mean values we can therefore 

 give as a practical rule, — 



"A rolled bar (of Swedish ores), whose curve has its greatest 

 curvature under a load = M Swedish pounds on the square deci- 

 mal line, tears when this load is increased 60 per cent, in the 

 case of iron, and in the case of steel when it is doubled." 



This practical rule is still more appropriate (provided that only 

 approximate determinations are concerned) if we remember 

 that the scales with which every rolled bar is coated just fall off 

 at the load which the bar bears in its passage through the point 

 of greatest curvature. Taking notice, then, of the load at which 

 scales fall off in quantity, we know that this load- in the case of 

 iron must be multiplied by 1 "6, and in the case of steel by 2'0 

 to obtain the load at which it would break. Hence in such a 

 case a direct measure of the permanent elongation is unnecessary. 



This practical rule obtains in the case of the kinds of iron and 

 steel of the most ordinary Swedish ores, and I have reason to 

 think that it may be extended to some kinds, at any rate, of 

 English iron. 



XXVI. Supplementary Researches in Hydrodynamics. — Part I. 

 By Professor Challis, M.A., F.R.S.,F.R.A.S* 



IN three articles contained in the Numbers of the Philosophi- 

 cal Magazine for June, August, and October 1862 — one 

 on the general differential equations of Hydrodynamics, and the 

 two others on the mathematical theory of the vibrations of an 

 elastic fluid — I have gone through a revision of the proofs of 

 the principal hydrodynamical theorems which I had given in 

 previous communications. The theorems were reconsidered 

 with reference more especially to their application in the Undu- 

 latory Theory of Light. Such application is made of them in 

 the December Number of the same year, in an Article entitled 

 "Explanations of phenomena of Light on the hypothesis of 

 undulations." The phenomena there explained are restricted to 



* Communicated by the Author. 



