556 



Report of Chemislry and Experimental Philosophy, [July 1 



pearance, according to the mode of pro- 

 curement ; generally speaking they are 

 white and chrystalline. 



The analysis of the constituents of yel- 

 low Indian corn, in the common and 

 dry state, is as follows : — 



Com.ftnte. JDry state. 



' 100. 99.980 

 At a late meeting of the Royal Society, 

 Sir E. Home communicated some observa- 

 tions on the influence of the black substance 

 in the skin of the negro, jn preventing the 

 scorching operation of the sun's rays. He 

 shewed that by exposing the back of the 

 band, and other parts of the body, covered 

 with thin white linen, to the direct influence 

 of the sun's rays, they become irritated and 

 inflamed ; small specks or freckles first 

 appear, and these, on continued exposure, 

 are followed by a vesicular separation of 

 the cuticle : the same happens when the 

 bare surface is exposed. When, however, 

 the part of the body thus exposed is cover- 

 ed with a piece of thin crape, though the 

 temperature of such part, when exposed to 

 the bright sunshine, exceeds that produced 

 upon the bare skin, the scorching and blis- 

 tering influence of the rays is entirely pre- 

 vented. Thus the deleterious etfect of the 

 sun's rays is prevented by an artificial 

 blackening of theskin, and perspiration be- 

 comes more copious, as is especially re- 

 marked in the uegro. 



Mr. ScoRESBY lately made- a series of 

 experiments on magnetism, which are fully 

 detailed in the Transactions of the Royal 

 Society of Edinburgh, of which Dr. Brews- 

 ter describes the following as the principal 

 results :^ 



1. Iron bars become magnetical by posi- 

 tion, excepting when placed in the plane 

 of the magnetic equator ; the upper end, 

 as regards the position of the magnetic 

 equator, becoming a south pole, and the 

 lower extremity a north pole. 



2. No attraction or repulsion appears 

 between a magnetized needle and iron 

 bars ; the latter being free from perma- 

 nent magnetism, whenevei* the iron is in 

 the plane of the ma»iietic equator ; couse- 

 qaently by measuring- the angle of no-at- 

 traction, in a bar placed north and south, 

 we discover the magnetic dip. 



3. Before a magnet can attract iron, 

 tliat is totally free from both permanent 

 magnetism and that of position, it iufuses 



into the iron a magnetism of contrary po- 

 larity to that of the attracting pole. 



4. A bar of soft iron, held in any posi- 

 tion, except in the plane of the magnetic 

 equator, may be rendered magnetical by a 

 blow with a hammer, or other hard sub- 

 stance ; in such cases, the magnetism of 

 position seems to be fixed in it, so as to 

 give it a permanent polarity. 



5. An iron-bar, with permanent polarity, 

 when placed any where in the plane of thfe 

 magnetic equator, may be deprived of its 

 magnetism by a blow. 



6. Iron is rendered magnetical ifscowcr- 

 ed or filed, bent or twisted, when in the 

 position of the magnetic axis, or near this 

 position ; the upper end becoming a south 

 pole, and the lower end a north pole ; but 

 the magnetism is destroyed by the same 

 means, if the bar be held in the' plane of 

 the magnetic equator. 



7. Iron heated to redness, and quenched 

 in water, in a vertical position, becomes 

 magnetic ; the upper end gaining south 

 polarity, and th? lo\yer end north. 



8. Hot iron receives more magnetism of 

 position than the same when cold. 



9. A bar-magnet, if hammered when in 

 a vertical position, or in the position of the 

 magnetic axis, has its power increased, if 

 the south pole be upward, 'and loses some 

 of its magnetism if the north end be up- 

 ward. 



10. A bar of soft steel, without magnetic 

 virtue, has its magnetism of position fixed 

 in it, by hammering it when in a vertical 

 position ; and loses its magnetism by be- 

 ing struck when iu the plane of the mag- 

 netic equator. 



11. An electrical discharge, made to 

 pass through a bar of iron, devoid of mag- 

 netism, when nearly in the position of the 

 magnetic axis, renders the bar magnetic ; 

 the upper end becoming a south pole, and 

 the lower end a north pole ; but the dis- 

 charge does not produce any polarity, if 

 the iron be placed in the plane of the mag- 

 netic equator. The efifects appesic to be 

 the same, whether the discharge be rtiade 

 on the lower or upper end of the bar, or 

 whether it is passed longitudinally or 

 transversely through the iron. 



1-2. A bar of iron possessing some mag- 

 netism, has its polarity diminished, de- 

 stroyed, or inverted, if an electric dis- 

 charge be passed through it, when it is 

 nearly in the position of the magnetic axis, 

 provided the south pole of the bar be down- 

 ward ; while its magnetism is weakened or 

 destroyed, if it receive the shock when in 

 the plane of the magnetic equator. 



13. Iron is rendered magnetical, if a 

 stream of the electric fluid be passed 

 through it, when it is iu a position nearly 

 corresponding with that of the magnetic 

 axis; but no effect is produced, when the 

 iron is in the p'.aue of the magueiic equator. 



We 



