402 WRITINGS OF JOSEPH HENRY. [1855-9] 



should be united in good metallic connection with the light- 

 ning-rods ; and in this case the perpendicular pipes convey- 

 ing the water from the gutters at the eaves may be made to 

 act the part of rods by soldering strips of copper to the metal 

 roof and pipes above, and connecting them with the earth 

 by plates of metal united by similar strips of copper to their 

 lower ends, or better with the gas or water pipes of the city. 

 In this case however the chimneys would be unprotected, 

 and copper lightning-rods soldered to the roof and rising a 

 few feet above the chimneys would suffice to receive the dis- 

 charge. We say soldered to the roof, because if the contact 

 were not very perfect, a greater intensity of action would take 

 place at this point, and the metal might be burnt through 

 by the discharge, particularly if it were thin. 



11th. As a general rule large masses of metal within the 

 building, particularly those which have a perpendicular ele- 

 vation, ought to be connected with the rod. The main por- 

 tion of the great building erected for the world's exhibition at 

 Paris is entirely surrounded by a rod of iron from which 

 rises at intervals a series of lightning conductors, the whole 

 system being connected with the earth by means of four wells, 

 one at each corner of the edifice. 



The foregoing rules may serve as general guides for the 

 erection of lightning-rods on ordinary buildings, but for the 

 protection of a large complex structure, consisting of several 

 parts, a special survey should be made, and the best form of 

 protection devised which the peculiar circumstances of the 

 case will admit. 



Numerous patents have been obtained in this country for 

 improved lightning conductors, but as a general rule such 

 improvements are of little importance. 



Such assumed improvements on the form of the lightning- 

 rod recommended by the French Academy in 1823 would 

 pre-suppose some important discoveries in electricity having 

 a bearing on the subject; but after the lapse of thirty years 

 the same Academy being called upon to consider the pro- 

 tection of the new additions to the Louvre finds nothing 

 material to change in the principles of the instructions at 

 first given. 



