376 WRITINGS OF JOSEPH HENRY. [1855- 



is rendered highly negative by the induction of a large cloud ; 

 and since this action takes place with as much efficiency 

 through the roof of a house and the chamber floors as it does 

 through the open air, a gas-pipe within a house, (in propor- 

 tion to its height) would powerfully attract any discharge 

 from a cloud in its vicinity. 



To obviate the danger from this source, the lightning-rod 

 which rises above the top of the building should be placed 

 in immediate metallic contact with the plexus of gas-pipes 

 outside the house. If as is very frequently the case, the rod 

 is made to terminate by simple insertion of a few feet in the 

 dry earth, while the gas-pipe is connected with miles of metal- 

 lic masses, rendered highly negative by induction, the path of 

 least resistance, or of most intense induction from the cloud to 

 the earth, will be down the rod to some point opposite the gas- 

 pipe, then through the house and down the pipe into the 

 great receiver below. This conclusion, from the theor}^ is 

 fully borne out by observation. On Friday evening, May 

 14, 1858, a house in Georgetown, D. C, was struck by light- 

 ning, and on Saturday, the next evening, another house was 

 struck in Washington, on Seventeenth street, north of Penn- 

 sjdvania avenue. The writer carefully examined the condi- 

 tions and effects in both cases, and found them almost identi- 

 cally the same. The houses were similarly situated, with 

 gable ends north and south, and attached to the west side of 

 each was a smaller back building. The lightning-rod of the 

 house at Georgetown was placed on the southern gable. It 

 terminated above in a single point, and its lower part was in- 

 serted into hard ground, through a brick pavement, to the 

 depth of about five feet. The lightning fell upon the point, 

 (which it melted,) passed down the rod until it came to the 

 level of the eaves, thence leaving the conductor, it passed hori- 

 zontally along the wet clapboards to the southwest eave or cor- 

 ner of the house, thence down a tinned iron spout to the tin 

 gutter under the roof of the back building, and thence it pierced 

 the wall of the house opposite the point on the outside of 

 the back building corresponding to the position of a gas-pipe 

 in the interior, after which no further effects of it could be 



