1862.] 105 



lit. " On the Difference in the Properties of Hot-Rolled and 

 Cold-Rolled Malleable Iron, as regards the power of re- 

 ceiving and retaining Induced Magnetism of Subperma- 

 nent Character." By GEORGE BIDDELL AIRY, Esq., F.R.S., 

 Astronomer Royal. Received April 22, 1862. 



(Abstract.) 



The author states that he had been desirous of examining whether 

 differences in the degree of change of subpermanent magnetism, such 

 as are exhibited by different iron ships, might not depend on the 

 temperature at which the iron is rolled in the last process of its 

 manufacture. By the good offices of Mr. Fairbairn he had received 

 gratuitously from Richard Smith, Esq., Superintendent of Lord 

 Dudley's Iron Works at the Round Oak Works near Dudley, twenty- 

 four plates of iron, each 1 6 inches long, 4 inches broad, and inch 

 thick ; twelve of which, after having been manufactured with the 

 others in the usual way, had been passed through rollers when quite 

 cold. Each set of twelve was divided into two parcels of six each, 

 one parcel being cut with the length of the bars in the length of 

 extension of the fibres of the iron, the other being cut with the 

 length of the bars transverse to the length of extension. 



For experimenting on these, a large wooden frame was prepared, 

 capable of receiving the 24 bars at once, either on a plane transverse 

 to the direction of dip at Greenwich, or on a plane including the 

 direction of dip. In some experiments, these planes were covered 

 with flag-stones, and the bars were laid upon the flag-stones ; in 

 others, the bars were laid immediately upon the wood. While there 

 lying, they were struck with iron or wooden hammers of different 

 sizes. The bars of the different classes were systematically inter- 

 mingled, in such a way that no tendency of the arm to give blows of 

 a different force or kind in special parts of the series could produce 

 a class-error in the result. For examination of the amount of polar 

 magnetism in each bar, it was placed at a definite distance (5 inches) 

 below a prismatic compass, which was used to observe the apparent 

 azimuth of a fixed mark ; the bar was then reversed in length, and 

 the observation was repeated in that state. 



The number of experiments was 2 1 . They were varied by differ- 



