1918.] The N.Z. Journal of Science and Technology. 
287 
of insulator shown in fig. 1 ; and whenever the line voltage exceeds 
80,000 volts it is necessary to employ a different type, which consists of 
a number of one-shell or two-shell insulators suspended in series one below 
Fig. 1 . — Main-line insulator, 66,000 volts, Lake Coleridge - Christchurch 
transmission -line. 
the other, the number of units used depending on the voltage of the 
circuit, and to some extent on the climatic condition prevailing in the 
district in which the lines are erected. This type is often employed for 
line voltage of 60,000 volts and under, but not as a matter of absolute 
