MAGNETISM 



179 



1422 



whereby about 20 Ibs. of stearine is consumed, 72 4 2 grains of magnesium -would 

 be required. The magnesium-wire can be easily prepared by forcing out the metal 

 from a heated steel press, having a fine opening at bottom ; this wire might be 

 rolled up in coils on a spindle, which would bo made to revolve by clockwork, and 

 thus the end of the wire, guided by passing through a groove, or between rollers, 

 could be continually pushed forward into a gas- or spirit-lamp flame, in which it 

 would burn.' 



In the reports of Mr. Brothers' experiments upon the magnesium-light, he says, 

 ' The result of an experiment I have just tried is, that in fifty seconds, with the 

 magnesium-light, I have obtained a good negative copy of an engraving, the copy 

 being made in a darkened room. Another copy was made in the usual way by day- 

 light, and in fifty seconds the result was about equal to the negative taken by the 

 artificial light. The sun was shining, but there was a good deal of fog in the atmo- 

 sphere.' 



Magnesium-Lamps have been invented and manufactured by 1?. W. Hart, London, 

 for photochemical and other purposes. This invention includes the use of springs 

 and wheels for self-acting propulsion and revolving of the ignited magnesium at the 

 same time, thereby avoiding a drooping light, which for optical illumination is a 

 great desideratum. These lamps are only made to order, as their mechanism is con- 

 sidered unnecessary for ordinary purposes, the action of the simplified lamp being as 

 follows : 



Hand-Lamp, for ribbon or one or more wires if more than one wire, they should 

 be twisted firmly together. Place the 

 end in the clip on the inside of the 

 flange of the reel A (Jig. 1422) ; ap- 

 ply a slight pressure to the reel by 

 turning the tension-screw T ; then 

 wind the magnesium on by turning 

 the flange with the finger and 

 thumb ; in the more highly-finished 

 lamps the winch, B, screws on the 

 spindle of A for winding on quantities 

 very regular. The loose end is then 

 passed through the guide and feed- 

 ing-rollers at F. Sufficient tension 

 having been applied by the screw- 

 head, T, the wire remains with- 

 out uncoiling. For use, release the 

 tension, and turn the winch, B, 

 towards the reel, A. In the self- 

 acting propelling-lamps above men- 

 tioned, a governor requires personal 

 adjustment to the rate of burning 

 in the simplified hand-lamps the 

 winch, B, is moved at the desired 

 rate, which saves a considerable ex- 

 pense for common purposes. The wire should be ignited in the smokeless part of a 

 flame, and a spirit-lamp is recommended. See Watts's ' Dictionary of Chemistry.' 



SVdAGETET, A bar of steel, which, being imbued with a peculiar condition of 

 electrical force, is possessed of polarity. The magnet has a special employment in 

 the mariner's compass, as from the undeviating way in which unless strong dis- 

 turbing causes are in operation it points north and south. The magnet is used also 

 in surveying-instruments. The use of iron in ship-building has led to a very careful 

 examination of the influence of iron on the ship's compasses. The late Dr. Scoresby, 

 Professor Airy, and some others, have been peculiarly distinguished in this important 

 inquiry, and to their memoirs on the subject the reader is referred. Magnetic 

 machines have been constructed for developing electricity, and employed for the de- 

 position of metals. See ELECTROMETALLURGY. 



XKAGiraTIC PYHETES. One of the native sulphides of iron. _Its chemical 

 composition is usually sulphur 40'15, iron 59'S5. Its power of attracting the mag- 

 netic needle is probably due to the peculiar condition in which the iron exists. It 

 is distinguished from the common pyrites (Mundic) by its inferior hardness and its 

 bronze colour. See PYRITES. 



MAGJJJETXSWT. A peculiar condition of electrical^ force. The phenomena of 

 magnetism which are rendered in any way available in the arts are detailed in 

 special articles ; as ELECTRO-TELEGRAPHY, &c. &c. All bodies must now be re- 

 garded as existing in one of two known conditions of magnetism. It is understood 



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