430 Miscellaneous Intelligence. 



Only two of the prismatic colors were visible. The red of the pri- 

 mary was succeeded by the green ; then came the faint red of the first 

 supernumerary bow ; a dark interval next occurred, which was follow- 

 ed by the still fainter red of the second supplementary arc. 



This singular optical phenomenon usually presents a succession of 

 green and violet ; or green and red arcs, alternating with each other, 

 like those seen by Brewster in 1828 ; but that supernumerary bows are 

 sometimes formed of a single hue, is evident from what has just been 

 stated, and from the case detailed by Prof. Twining, who beheld, at 

 Montreal, in September, 1823, ihree supplementary bows of a violet or 

 dull red tint, unaccompanied by arcs of green. 



4. On some Recent and Remarkable Examples of the Protection af- 

 forded by Metallic Conductors against Heavy Strokes of Lightning ; 

 by Sir W. S. Harris, (Proc. Brit. Assoc, 1847, Athenaeum, No. 1027, 

 July 3.) — The possibility of guarding buildings and other structures 

 against the destructive effects of lightning, has been made a great 

 question in practical science, from the time of Franklin to the present 

 day ; and it is of considerable public importance, seeing the frequent 

 damage which occurs to our beautiful churches and other edifices by 

 strokes of lightning, to bring this question completely under the domin- 

 ion of induction, observation and experiment. The general principles 

 which Sir W. S. Harris submitted as deducible from the inquiries to 

 which he alluded are these : — If we imagine a ship or building to con- 

 sist altogether of metallic substances, it would certainly be secure from 

 any damage by lightning and for this simple reason, that what we call 

 lightning is the result of the electrical agency forcing a path through 

 resisting matter such as the air, and extricating, with explosive and ex- 

 pansive force, both light and heat in its course. When, on the con- 

 trary, it falls upon comparatively non-resisting bodies, such as the 

 metals, then this form of lightning vanishes, and the discharge assumes, 

 if the metallic body be sufficiently capacious, the form of a compara- 

 tively quiescent current. Our object should be, therefore, in defending 

 any building or ship from lightning, to bring the general mass so tar 

 as possible into that 

 would have supposing 



passive or comparatively non-resisting state 

 it a mass of metal. This is, in fact, the single 



and simple condition of such an application, without any reference 



- ri 7 •" — wers 



__ t'U 



manifested by certain bodies for the matter of lightning, and whic i 



whatever to assumed forces of attraction or peculiar specific pov 



really do not exist. This simple principle, by a careful mecha " lC h a g 

 arrangement calculated to render it practical and applicable to all * 

 duties which the general structure of a ship together with its masts 

 to perform, is now universally carried out in the navy, with the mo 

 perfect success ; so that damage by lightning in the vessels so n 

 has, for the last fifteen years, quite ceased. The masts are made com- 

 pletely conducting by capacious plates of copper, reaching fr° m 

 highest points to the keel ; and are tied into one general conn ^ the 

 with all the great metallic masses employed in the construction o 

 hull, and united by large bolts of copper passing through the kee ^ 

 sides, with the copper expanded over the bottom and with the ' ^ j 

 is quite impossible that a discharge of lightning can fall on lhe **\ org 

 in any place, and not be at once transmitted safely by the cond 



