-1859] WRITINGS OP JOSEPH HENRY. 379 



The different sides of a building are not all equally ex- 

 posed to accident from lightning. Thunder-clouds in this 

 latitude approach us from the southwest, and hence the part 

 of the house which faces this direction is not only more ex- 

 posed to the fury of the storm, but also to the effects of the 

 electrical discharge. The position then of the lightning-rod 

 on this account is not to be neglected. The soot which lines 

 a chimney is a good conductor, and hence the discharge not 

 unfrequently passes into the house along the interior surface 

 of this opening. But there is another circumstance which 

 renders the chimney still more liable to be struck, namely, 

 the column of heated air and smoke which ascends from it 

 into the atmosphere when there is a fire burning below. 

 These are tolerably good conductors of electricity, and as the 

 latter may under some conditions extend to a considerable 

 height in the atmosphere, they are sufficient to attract the 

 descending discharge and determine its course to the chim- 

 ney. A rod should therefore be placed on every chimney 

 through which a column of heated air ascends during the 

 season of the occurrence of thunder-storms. 



Among the many novel propositions urged upon the 

 attention of Congress there was one a few years ago with re- 

 sults having a bearing on this subject. For the purpose of 

 lighting the public grounds an appropriation was made to 

 erect a mast eighty feet in length on the top of the dome of 

 the Capitol. This mast was surmounted by a lantern of about 

 six feet in height and of corresponding diameter, containing 

 a large number of gas-burners, and terminated above by a 

 gilded copper ball of about a foot in diameter. After this 

 gigantic apparatus had been erected in defiance of all the 

 principles of architecture and illumination, the author of this 

 report was called upon for his opinion as to the effect of 

 lightning upon it. The answer given was that since the 

 simplest method of obtaining electricity from the atmosphere 

 is to elevate a piece of burning tinder on the end of a fishing- 

 rod, the apparatus placed on the dome of the Capitol would 

 be a collector of electricity on an immense scale, and there- 

 fore would probably be struck by lightning. As if to verify 



