HISTORY AXD PROGRESS. 187 



But it is questionable if this method is so good as that of 

 Boucherie, as it is necessary to force the solution into the 

 wood at right angles to its tubes, thereby injuring its strength 

 and letting the sap, which is the immediate cause of decay, 

 remain ; the coagulation of the albumen in the sap, to 

 any material depth below the surface, being a matter of 

 doubt. 



The method adopted by Sir Charles Bright is to have the 

 poles well charred from the lower ends to a foot above the 

 depth to which they are destined to be fixed into the 

 ground, and the charred parts soaked in gas-tar for about 

 twelve hours, the poles standing in tanks of tar, in a timber 

 framing. 



The sap ingredients being the prime movers in the rotting 

 of dead wood, the idea has occurred to put up insulators on 

 the stems of living trees a method which has been found to 

 answer well in Switzerland, America, and in some parts of 

 Germany, where trees are to be found at convenient distances. 

 The only drawback to this system is, the violence with which 

 trees are sometimes moved in heavy storms. To obviate 

 this difficulty, Lieut.-Col. Chauvin has constructed a swing- 

 ing insulator, which will be described afterwards. 



Wooden posts invariably decay first at the ground level 

 "the wind and water line" where the surface is moist and 

 in contact with the air. A method of retarding the decay 

 by sheathing the post at this part has been tried in India 

 with comparative success, the lower end, to a certain height 

 above the ground, being covered by an iron casing. In 

 Bengal such a line was erected, the posts being of large 

 bamboo canes and the protection of the lower parts cast-iron 

 sockets. 



This brings us very near to a suggestion which has been 

 much advocated that of dispensing with wood, and con- 

 constructing the posts entirely of iron, whose durability is 

 so superior. The greater cost of such posts is the only 

 objection to them. 



Pillars of stone, or mason's work, would undoubtedly not 

 only last longer, but would be less liable to accidents by 



