Manchester Memoirs, Vol. hnii. {\gi^), No. H. ii 



in air velocity they shew the great superiority of the 

 Brabbee tube over any other form of side gauge except 

 that which is flush with the pipe wall. The disadvantages 

 of the latter are very apparent For, firstly, in a commercial 

 pipe system it is utterly impracticable to bore holes at 

 all sorts of places for pressure measurement, and to 

 render pipes in such holes absolutely flush with the inner 

 duct surface. Another disadvantage lies in the im- 

 possibility of getting a pressure measurement at the same 

 point as the velocity measurement, which is sometimes 

 of considerable importance. 



The Brabble tube combines the pressure and velocity 

 tubes in a single portable and accurate apparatus, which 

 can be inserted at any hand hole or other accessible place 

 in the air circuit. 



Tests on Accuracy of Position. 



It will be realised that where tubes like the Brabbee, 

 Nipher or Pneumometer (see Fig. 5) are used, the position 

 of the tube with respect to the pipe conveying the air may 

 make a considerable difference. I made a few tests on this 

 matter with the disc gauge, the Brabbee tube, and the 

 Nipher collector by placing each in turn in the air pipe 

 at a particular place, and keeping the air conditions con- 

 stant. In the first instance each tube was set as accurately 

 in its proper position as careful measurements would 

 allow, and having taken pressure readings by this means 

 the tube was moved through various angles to ascertain 

 the effect on the pressure measurement of errors in setting. 

 The angles were not very carefully measured, because the 

 result of even a small movement of one or two degrees 

 was sufficient to show that the Brabbee tube was the only 

 one which gave readings of even approximate consistency, 

 I believe that in the setting of this tube (as far as pressure 



