296 Miscellaneous Intelligence. 
a principle as to whether its accession and diminution is the effect pro- 
duced by distance, transits of opaque bodies, or solar spots; or whether 
the nebulosity surrounding 7 Argus interferes with the light emitted by 
the star; if so, the increase and diminution, however vacillating, become 
obvious. 
VI. MISCELLANEOUS SCIENTIFIC INTELLIGENCE. 
manufacture necessarily awakened much interest here. Thinking there- 
fore that your readers may feel a like interest, I take the liberty of sending 
e 
Rupert’s drop. In the case of solid cast iron shot, for example, there is 
maximum diameter within which these can be cast without containing 
cavities. But beyond this point, the contraction toward the exterioh 
which is the first to solidify, is so great that these cavities are 
Ia general the contraction is irregular and the cavities are near the upper 
surface. Hence it is considered preferable to cast thick shells, in whieh 
ease the core locates the cavity exactly in the centre. For the same 
ficulties in casting large guns, it was at first proposed to apply the same 
remedy. 1at is, to cast the gun with a core, so that the contraction 
should be uniform from the axis to the surface. | 
ajor—then Lieutenant—T. J. Rodman had his attention first called 
: maker” was a wrought iron imported gun, having a bore 7 “ans 
inches in diameter. Considering the conditions under which 1rom § 
were usually cast, Major Rodman at once saw the enormous strain ” 
cast was In ta enter” 
He then applied himself to the mathematical investigation 
the conditions under which a central force acts. He found that Barlow 
us in a gun one calibre thick the distance from the bore to teenie 
is 8, and the strain on the exterior when fired is only th that om ef 07 | 
terior. Now if the strain at the interior is the breaking strain, then ' a 
