TRANSACTIONS OF THE SECTIONS. 33 



opening? made in the side of the flue or chimney. The draught of air entering by 

 this hole gives revokition to the fan, and tlience, by means of an endless screw and 

 toothed wheel, to a crank which moves a bellows-pump. This draws air from the 

 flue or chimney by means of a tube inserted through the brickwork, and causes it 

 to pass through the absorption-bottles. The whole is portable, being enclosed in a 

 small box, except only the fan, which projects about three inches. 



On an Ether Anemometer for Measurinri the Speed of Air in Flues and Chimneys. 



Bij A. E. Elktcher, F.'O.S. 



This instrument is contrived for measuring the speed of air in pipes, flues or 

 chimneys in cases where, from the presence of heat, soot, or corrosive vapour, a 

 delicate mechanism would be inadmissible. It has been called an ether-anemo- 

 metei-, since ether is employed in its construction ; by it the speed of air moving 

 at any greater rata than that of nine inches per second can be measured. 



The principle employed in its construction is in part that of the Gifford's injectoi', 

 •wherein a current of steam passing the open end of a tube is made to produce a 

 partial vacuum in it. 



In the current of air whose velocity is to be measured, is placed a glass or metal 

 tube with a plain straight end, and along with it a tube whose end is bent at right 

 angles and cut off short. This bent end is turned to face the current, while the 

 straight tube is so exposed to the current that it passes along its open end. _ The 

 difference of pressure in these two tubes will then be a measure of the velocity of 

 the cm-rent. The pull or suction of the chimney will be the same in each. 



To measure this difference of pressure, which for slow currents is very small, 

 many methods were tried until the present form of apparatus was adopted. It is 

 but a modification of the U-tube;'the limbs are cylinders of three inches in dia- 

 meter and four inches in length, connected at the bottom by a small horizontal 

 tube. The liquid used is ether, on account of its low specific gra-s-ity aud its mo- 

 bility. In each limb is a hollow metal float, scribed with a fine line. The level of 

 these lines is read off" by a finely divided scale and vernier adjusted by fine screws. 

 It is easy to read to ygVo i^ch, and therefore to measure a pressure which is balanced 

 by a column of ether ^ Jg-j^ inch high. 



' In order to learn how to connect the readings of the instrument with the speed 

 of the air operating on it, it was determined not to depend on calculation only, but 

 to test it against currents of air of known speeds. For this purpose a pipe was con- 

 structed fourteen inches diameter and 100 feet long, one end being in connexion 

 with a tall chimney, the other one open. At the open end a hot brick was placed, 

 and at a given sig'nal a drop of sulphuric acid was allowed to fall upon it. The 

 cloud of vapour thus raised passed along the pipe, and its arrival at the distant end 

 was observed on looking through two holes bored for the purpose. The time was 

 noted by a watch held to the ear. Having thus ascertained by two or three trials 

 the speed of the' air, readings from the ether-anemometer were taken. The speed 

 was then altered by means of a slide or damper, and measured again by noting 

 accurately the time taken by the cloud of vapour in travelling tlie 100 feet, and a 

 fresh reading of the anemometer registered. In this way a Table was made enr- 

 bracing the greatest range of speed obtainable by the chinmey. 



It was clear from the law of bodies in motion, that this should obey the formula 

 p = v-Xc; where;; = the indication of tlie instrument, v = velocity of the current, 

 and c some constant influenced by the individual details of the instrument. From 

 the series of experiments thus made, the value of c was found to be 25-31 : with 

 this a complete table of the values of ;j from 0001 inch to 1-000 inch was calculated. 



The instrument is found to be very satisfactory and reliable in its indications. 



It may also serve as a wind-gauge. A plain piece of iron gas- pipe projecting 

 vertically above the roof of the hou'se or observatory, should communicate with 

 one limb of the ether-anemometer. As the wind blows over the open end of this 

 pipe, a partial vacuum would be formed and measured by the instrument. _ An 

 advantage of tliis arrangement over the wind-gauges at present in use would lie in 

 the absence of all moving parts whose friction might vary, and which might pos- 

 sibly be deranged. 



1867. 3 



