HYDRO ELECTRIC INSTALLATIONS. LXVII. 
Poles.—In a country which produces splendid hardwoods 
it seems sacrilege to suggest that steel lattice towers 
should be used, but the tendency in other countries is all 
in that direction. Steel towers or lattice poles spaced 10 to 
the mile are not much more expensive than wooden poles 
40 to the mile, taking into account the shorter life of the 
wood and the greater number of insulators and pins. 
Wooden towers could be used, but white ants and bush 
fires are against the use of wood. Long transmission 
lines have to be efficiently patrolled, and in this respect 
Australia is more favourably situated than in countries 
like South Africa and India, were mischievous or hostile 
natives may give trouble. In the Cauvery Falls to Kolar 
gold fields line in southern India, the natives found that the 
voltage on the telephone wire was not dangerous, and stole 
it, until the engineer hit upon the plan of putting high 
pressure on the line during the night time. 
Insulators.—To insure that there shall be no internal 
defect, large porcelain insulators are usually made in two 
or three parts cemented together, and sometimes one 
part is of glass. The petticoats are usually about the 
same diameter, arranged one above the other so as to give 
necessary axial length. The break down test is made at 
double the working pressure, and carried out by placing 
the insulator in an inverted positionin brine. The pin hole 
is also filled with brine and the pressure applied between 
the two. The test for non-absorbent quality of the 
porcelain is to break the insulator into small pieces and 
weigh after drying at 212° Fah. The pieces are then 
steeped in water for 24 hours, weighed again and if there 
be any difference in weight the batch of insulators is 
rejected. 
Iron pins cost more than wood, but the total cost of pins 
is only asmall percentage of the total cost ofa transmission 
