70 feet. 



270 ^Ir.W. Sturgeon on the Distribution and Retention 



help to balance the middle part {b) : — a circumstance not 



considered in the ex- ^ ; _ ; 



periment brick, and in- — ^-^ ^— ^ 



deed too trifling to af- 

 fect the conclusion here 

 drawn. So that a brick 

 82^ feet long 

 38 — wide 

 8 — deep, of the same strength of materials as 

 the experimental bricks, would carry something more than its 

 own weight, but would weigh 134-0 tons. 



Yours trul}', John Southkrn. 



N.B. The common bricks were about 6| inches long, '^^■j, 

 broad, and 2f deep. 



[To be continued.] 



XXXIX. On the Distribution and Retention of Magnetic 

 Polarity in Metallic Bodies. By W. Sturgeon, Lecturer 

 on Experimental Philosophy at the Honourable East India 

 Company's Military Academy, Addiscombe* . 

 [With a Plate.] 



T^HE retention of magnetic polarity in hardened steel is so 

 ^ very strikingly manifested in artificial magnets of various 

 forms, and the circumstance is so well known, that it would be 

 quite unnecessary in this place to advance any remarks con- 

 cerning it, further than merely to name it, for form sake, in 

 the order in which it stands, and the pre-eminent rank which 

 it universally holds amongst the metals, as to the display of 

 this mysterious faculty. 



The retention and distribution of magnetic polarity in other 

 metals, however, are by no means of such general notoriety ; 

 peculiar modes of experimenting are required for their exhi- 

 bition, and but very few of their phenomena have yet had 

 recognition beyond the sweep of the curious eye of the phi- 

 losopher. 



In my last communication f I had occasion to allude to the 

 retention of magnetic polarity, (or the residual polarity, as I 

 there called it,) displayed in soft iron, which had previously 

 been excited to an exalted degree of intensity. My remarks 

 in that communication, however, were confined to soft iron in 

 bars, in the various forms in which it is usually employed as 

 electro-magnets. In the present, my observations will be ex- 

 tended to the retention, and also to the distribution of magnetic 



• Conimunic-itcd by the Author. 



f See our last Number, p. 194. — Ewx, 



polarity 



