374 Mr. Mallet on the Physical Conditions 



Note O.— (Sect. 181.) 



It appears that cast-iron field-guns have been in use in the Swedish and Danish services 

 since 1831, the first trials dating back to 1804; and that now, after several years' expe- 

 rience, they are preferred to bronze guns by the Artillery of both countries. See Jacobi, 

 " Sur I'Etat actuel de FArtillerie Swedoise," 1849. Cast-iron field-guns have been tried 

 in Sweden as far back as 1805; and in 1848 their horse artillery was armed with such 

 guns. Some Swedish and Danish cast-iron field-guns were placed in the Exhibition of 

 1851, amongst which were — A Swedish 6-pounder, 5 ft. 5-75 ins. long; 3-828 ins. caliber; 

 charge, 2 lbs. 7 oz. ; weight of gun, 803 lbs. The British bronze gun of same class weighs 

 G72 lbs. A Danish 6-pounder, 5 ft. 3-5 ins. long; weight, 874 lbs. 



In the United States, cast-iron 6-pounder field-guns have been employed at least since 

 1844. They are from the established models of bronze guns of equal caliber, but in- 

 creased in thickness at the breech part, without corresponding increase of weight, by a 

 certain reduction of thickness towards the muzzle. The successful use of these cast-iron 

 field-guns would appear to dispose of many of the objections that have been groundlessly 

 urged (even by some of the local artillery authorities in the United States), and by others, 

 against the advantageous application o( wronght-iron to the same purpose; for very many 

 of the objections, for example that of corrosion, apply equally to both, or with greater force 

 to the former. 



Note P.— (Sect. 190.) 



A VERY remarkable instance of the internal tensional strains produced in cast-steel, in the 

 process of hardening or tempering, has, since the text was written, met my eye in the 

 pages of the "Franklin Journal," vol. viii., p. 133, in which a tolerably large cylindrical 

 pivot for a shaft, with a hole through it too, in the axis of the cylinder, burst or split into 

 two or more pieces, some time after having been hardened, with a noise nearly equal to 

 that of a pistol-shot, and throwing the fragments several feet. The external edges of the 

 fractures presented an arrangement of minute crystals penetrating its substance perpendi- 

 cular to its external contour (like those of chilled cast-iron) ; thus proving that in steel, 

 also, — although, from the minuteness of the crystals, much less marked, and generally 

 scarce distinguishable, — the aggregation of its particles follows the general law announced 

 in the text. 



The steel guns, made and tried, by the Hanoverian and other German Governments, 

 were all of small caliber, and their proportions much about the same as those of bronze 

 guns; indeed, a 12-pounder, repeatedly proved at Woolwich, a year or two since, with 



