Lightning Conchicturs in Ships. 163 



which will transmit the electric matter directly through the 

 keel *, being the line of least resistance. 



16. From what has been already observed, it will be appa- 

 rent, that, in whatever position we suppose the sliding-masts to 

 be placed, whether in a state of elongation or contraction, still 

 the line of conduction will remain perfect, for that part of the 

 conductor which necessarily remains below the cap and top, 

 when the sliding masts are struck, is no longer in the line of 

 action, consequently its influence need not be considered. 



18. The following table exhibits the mean proportion of a 

 conductor thus constructed on one mast of a fifty gun frigate, 

 as compared with the copper links usually furnished to the Bri- 

 tish navy, together with the necessary equivalent in copper or 

 iron bolt, in order to obtain a conductor of the same mass. 



The resulting quantities in the last line at the bottom of the 

 table, represent, with the exception of the proposed conductors, 

 the masses, surfaces, and diameters of cylindrical metallic rods, 

 supposed to extend the whole length of the mast. Thus in 

 column 2, we have the diameter and surface of a copper rod, 

 containing 2423 cubic inches of metal, being an equal quantity 

 of matter to that in the proposed conductors, and from which it 

 is calculated. The sums, therefore, are not the result of the 

 addition of the successive masts. The same may be observed 

 in column 3 ; taking the equivalent in iron. In the third and 

 fourth columns, we have the mass and surface of a copper rod 

 of half an inch in diameter, generally allowed to be adequate to 

 any shock of lightning yet experienced : and, lastly, in co- 

 lumn 4, we have the mass and surface in the conductors now 

 furnished to the British navy ; which we find, as compared 

 with the mass in the proposed arrangement, is only as 94.4 : 

 2423. 



• Since the mizen-mast does not step on the keelson, it will be necessary 

 to have a metallic communication at the step of the mast with the perpen- 

 dicular stancheon immediately under it, and so on to the keelson as before, 

 or otherwise carry the conductor out at the sides of the vessel. 



l2 



