436 M. Gau-Lussac on [Dec. 



ground by means of the conductor which is attached to its foot. 

 Fig;. 24 is a steeple with the paratonnerre stem fixed to the 

 cross. Churches not defended by a paratonnerre on the steeple, 

 require stems from \o to 24 feet high, similar to that of a flat 

 building. 



Fig. 25 represents a paratonnerre so constructed as to be 

 ornamental, with a vane, ike. 



P aralonnerres for Powder Magazines, 



These of course require to be constructed with the greatest 

 care, but in principle are perfectly similar to the one we have 

 described at length. They should not be placed on the build- 

 ings, but on poles at from 6 to 10 feet distance, fig. 26. The 

 stems should be about seven feet long, and the poles of such a 

 height, that the stem may rise from 15 to 20 feet above the top 

 of the building. It is also advisable to have several paraton- 

 nerres round each magazine. If the magazine be in a tower, or 

 other very lofty building, it may be sufficient to defend it by a 

 double copper conductor, ABC, fig. 27, without any paraton- 

 nerre stem. As the influence of this conductor will not extend 

 beyond the building, it cannot attract the lightning from a dist- 

 ance, and yet will protect the magazine, should it be struck. A 

 common magazine, or any other building, may be defended in a 

 similar manner, fig. 28. 



Paratonnerresfor Ships. 



The stem of the paratonnerre for a ship, fig. 29, consists 

 merely of the copper point, A C, fig. 4, already described. It 

 is screwed on a round iron rod, C 13, fig. 30, which enters the. 

 extremity, I, of the pole of the top gallant mast, and carries a 

 vane. An iron bar, M Q, connected with the foot of the round 

 rod, descends down the poie, and is terminated by a crook, or 

 ring, Q, to which the conductor of the paratonnerre is attached, 

 which, in this case, is formed of a metallic rope, and is supported 

 at intervals by rigging, g g, fig. 29, and after having passed 

 through a ring, b, fixed to the chains, is united to a bar 

 or plate of metal, which is connected to the copper sheathing on 

 the bottom of the vessel. Small vessels require only one para- 

 tonnerre ; large ships should have one on the mainmast and 

 another on the mizenmast. 



General Disposition of Paratonnerres on a Building. 



It is allowed from experiment, that the stem of a paratonnerre 

 effectually defends a circle of which it is the centre, and whose 

 radius is twice its own height, from lightning. According to 

 this rule, a building 60 feet long, or square, requires only a single 

 stem of 15 or 18 feet, raised in the centre of the roof, figs. 14 

 and 17. In tig. 17, the conductor is a metallic rope. 



