﻿Air Velocity by means of Hot Wire Anemometer. 559 



only requires the electrical contact at these points to be 

 moderately good. The tension in the wire is adjusted by a 

 fine silk thread carried down from each of the brass blocks 

 to an adjustable screw in the centre of the ebonite block ; 



Fig. 2. 



Details of Fork for holding Anemometer-Wires and Potential 

 Terminals. 



[The wire is shown in position over an end of a channel of rectangular 

 cross-section, and illustrates the guard-ring effect obtained by the 

 use of potential terminals fused to the wire.] 



this thread is also effective in preventing lateral vibrations 

 of the fork. Carried up from each end of the ebonite block 

 are two thin steel strips crossing each other to the opposite 

 arms of the fork, insulated from each other and also from the 

 fork by means of thin mica strip. These steel strips, which 

 are held in position along the arms of the fork by two 

 lashings of fine waxed silk cord, serve to brace the fork and 

 at the same time serve as potential leads ; at each end is 

 soldered a small brass block drilled to hold a fine needle at 

 the extremity of which is soldered a short length of 6-mil 

 platinum wire. To these are soldered one extremity of the 

 1-mil platinum potential terminals, the other being fused to 

 the anemometer-wire ; this is most easily accomplished by 

 connecting the wire to the bridge connexions and adjusting 

 the current until it is at a bright red heat ; the potential 

 wires are then brought to the required position and wound 

 twice around the anemometer-wire ; by applying a slight 

 tension while this is being done, a satisfactory fused contact 

 will be effected. The free end should then be broken or 

 cut off close to the anemometer-wire, so as to diminish the 

 cooling effect of the potential leads. The heating to which 

 the wire is subjected during this operation serves to anneal 

 it sufficiently well for permanent use. 



In the course of experiments by the writer on the How of 

 air between parallel planes, considerable experience has been 

 acquired as to the most suitable method of employing the 



