98 HALIFAX WATER WORKS. JOHNSTON. 



conduit, rebuilt ,in 1886, is 1,300 feet long, 3^ feet wide and 4J 

 feet high, built of 4-inch by 4-inch hemlock deal, with four 

 manholes throughout its length. Its upper end is at an eleva- 

 tion of 196.20, with a fall to Chain Lake of six inches. 



Ice. 



The experience with, the formation of a'achor ico has been 

 similar to that of other places. With a sheet of open water at a 

 temperature of 32 degrees F., and the temperature of the air 

 varying from 5 degrees to 20 degrees above zero, and a high 

 wi'nd blowing, the ice forms in small detached needles or crys- 

 tals. Thin portions of it accumulate in spongy masses and float 

 along at or below the surface, their specific gravity differing 

 but little from that of water. They adhere readily to all solid 

 bodies with which they come in contact, and grow rapidly when 

 once they have secured a centre of crystallization. It will not 

 form in bright sunshine on the contrary, it rises to the sur- 

 face in spongy masises, and when the surface freezes over it 

 lets go its grip. The lee side of a reservoir gets most of its 

 anchor ice, and whenever we have been troubled with it the 

 wind has always been from a north-westerly direction. Between 

 1883 and 1893 ; no trouble was had from ice, and it is thought 

 that this was due to the fact that a screen of stout pickets 

 driven into the bottom, capped on top with a boom rising a'nd 

 falling with the level of the water, was placed in front of the 

 gate houses. In 1892 this was removed, and on the llth 

 December of that year ice closed the sluice gate at the south 

 gate-house cutting off the supply to the 24-inch main, and con- 

 tinued until four o'clock in the morning, when the wind sub- 

 sided, and the ice stopped running. In. 1898 the filter wall 

 already referred to was built in front of the south gate-housa, 

 but ice formed inside the wall, and there was danger that the 

 gate-house would freeze up solid, so the screens were removed 

 until the danger had passed. This is the last time there has 

 been any trouble from it. 



