. Engineering and Contracting . onstruction in practice requires both careand experience. For example, the exact tension to whicha line must be set depends on the temperature existing atthe time. Care must he exercised in determining that terft-perature. as the temperatures of the wire and the surround-ing air may differ appreciably. Again the wireman adjustsIhe tension of the line during erection, but it is usually ad-visable to check his work. The tension and sag of the wirebeing definitely related, one method is to measure the sagof the line between the poles by marking a distance equalIc t
. Engineering and Contracting . onstruction in practice requires both careand experience. For example, the exact tension to whicha line must be set depends on the temperature existing atthe time. Care must he exercised in determining that terft-perature. as the temperatures of the wire and the surround-ing air may differ appreciably. Again the wireman adjustsIhe tension of the line during erection, but it is usually ad-visable to check his work. The tension and sag of the wirebeing definitely related, one method is to measure the sagof the line between the poles by marking a distance equalIc the correct sag downwards from the insulators on each Moscow Water Supply.—According to the London Timesthe water supply system of Moscow has broken down underSoviet control. SO per cent of the houses being without 1,400 cases of typhus were occurring weekly. The sys-tem draws water by a large pumping station on the MoskvaRiver, supplying 150 million litres daily, and 1,315 men arestated to be employed in the 12 14 16 18 20 22 24- 26 28 30TIME (in ss-is.) OF 20 WA VESCurves Connecting Tension and Vibration Period. pole and noting whether the lowest point of the wire fallsin the line of vision joining the two marks. An entirely dif-ferent method consists in determining the natural time ofswing of the line considered as a pendulum. The sag variesinversely as the square of the period of oscillation and thelelationship is independent of the material of the conductoror length of span. This method has been used with successon heavy power wires with short spans and considerablesag: but according to an article in the Post-Office ElectricalEngineers .Journal by Mr. A. C. Timms, the method was oflittle use on the comparatively small wires used on themain trunk telegraph or telephone lines of the British armiesin France. The wires were chiefly 100 lb. copper with someof 150 lb. and 200 lb., and usually the wiremen had a tend-ency to pull them up too tightly. Mr. Timms
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