Chemical Science. 47t 



if there be ten. A scale will be thus formed of magnetic intensi- 

 ties, corresponding^ to a fraction of any ^ven discharge. If afterJ 

 wards, instead of using different branches of the same metal, similar 

 wires of different metals be used, and a second discharge be passed 

 through this new system, equal to one of known effect, it will be 

 divided unequally between the wires, and the steel needles placed 

 transversely across them will indicate by their degree of magnet- 

 ization, whether a particular metal has transmitted a third, anothei* 

 a fourth, another a tenth, or any other proportion of the whole 

 quantity of electricity discharged. — Ann, de ChimiCy xxxiv. p. 7. 



2. On Lightning Rods and Compasses, by Dr. Fi<icher. —^Dr. Fischer 

 states, that when iron is magnetised it loses much of its conducting 

 power for ordinary electricity; and concludes from his observations, 

 that iron, which is known to become magnetic by even feeble elec- 

 tric explosions, is a very improper metal for the construction of 

 lightning-rods. He relates an instance in which a rod of this 

 metal, placed as a lightning-conductor upon a powder-magazine, 

 had entirely failed on several occasions in preventing the explosion 

 of lightning close by its side. Upon examining this rod, it was 

 found to have attractive and repulsive magnetic properties. 



M. Fischer consequently recommends copper as the metal to be 

 used, and advises that the end be gilt or made to terminate in a 

 gold point, rather than with platina, because the former is so much 

 superior in conducting power. 



The conclusions of M. Fischer with regard to the decrease of 

 conducting power in iron, when magnetised, are in singular contrast 

 to the assertions of Mr. Abraham, who states that the conducting 

 property is wonderfully increased by making iron magnetic, and 

 recommends that all lightning-rods be of magnetised iron. We 

 doubt whether any effect is produced either way. 



Mr. Fischer endeavours to prevent the disturbance of the mag- 

 netic needle from neighbouring masses of iron, by placing it in a 

 bowl of that metal of equal thickness throughout. He states, that 

 the needle points north and south, and is not effected by the approx- 

 imation of iron. The means are the same, generally, as those prac- 

 tised some years ago in this country by Mr. Jennings, who sur- 

 rounded his needles with a strong ring of iron. The effect is also 

 stated to be the same. — Bull. Univ. E. vii. 93. 



Mr. Abraham used two cast-steel rods, properly hardened and 

 tempered, each three feet in length and half an inch in diameter; 

 one end of each bar was hammered to a fine point, and one bar 

 was rendered magnetic ; then a brass ball was placed two inches off 

 from the prime conductor of a machine, and the points of the un- 

 magnetised and magnetised bars brought alternately towards it; 

 the magnetic bar (it is said) prevented the passage of sparks 

 between the conductor and ball when it was twelve inches off^ 

 whilst the other required to be brought to within nine inches. — 

 Phil. Mag. N. S. i. p. 267. 



