TRANSACTIONS OF SECTION A. 



'279 



10. An Anemometer for Measuring the speed of Smoke or Corrosive Vapour. 

 By Alfred E. Fletcher, F.C.S. 



In the year 1869 I had the honour of reading a paper descriptive of an 

 anemometer I had contrived for measuring the speed of currents of air, which, 

 being highly heated or containing corrosive gases, forbad the use of the instruments 

 hitherto in common use. These all have moving parts, wheels, pivots, &c, which 

 would be destroyed or rendered useless by great heat or acid vapours. 



My anemometer consists of a bent tube and a straight one, which, together, are 

 thrust into the current whose velocity is to be measured, the outer ends of the 

 tubes being connected by means of flexible tubing with a delicate manometer for 

 determining the difference there may be between the pressures exerted in the two 

 tubes. 



The manometer I prefer, and which I have for many years constantly used, 

 is a simple U tube partly filled with ether. One of the flexible tubes being 

 connected with each limb of the U tube, the position assumed by the ether is an 

 indication of the difference of the pressures exerted on it. If the pressures are 

 equal, the surfaces of the ether in the two tubes remain level one with the other. 

 To measure the deviations from this normal position, finely-divided scales provided 

 with a vernier are employed. In the hands of some who use the instrument, so 

 fine a measurement is found to require too delicate handling, and too close an 

 observation. To obviate this, or to assist the observer, I have introduced in the 



