Manchester Memoirs, Vol. Iviii. (19 14), No. 7. 7 



inclinations, viz., 1/20 and 1/4. These give corresponding 

 multiplications. The fluid used was alcohol of specific 

 gravity 08. The gauge can be read easily to | m/m., 

 and this corresponds therefore to approximately 1/40 m/m. 

 or 1/1200 inch. An interesting point is that with such 

 readings no ordinary glass tube is sufficiently accurate, 

 and the scale must be made to the instrument to counter- 

 act irregularities in the bore of the tube. 



The following tips were selected for tests : — 

 (i) A disc gauge exactly like that of Heenan and 

 Gilbert. 



(2) A disc gauge with a tin disc 2^ in. diam. 



(3) A disc gauge „ „ ifin. „ 



(4) A Nipher collector. (Fig: 2.) 



(5) A Brabbee tube. (Fig;: 3.) 



(6) A side tube 1/16 in, diameter, with orifice flush with 



the pipe wall. 



The Nipher and Brabbee tubes were included because 

 they are the latest instruments in use in Germany for the 

 purpose. The side tube was used for two reasons : 

 firstly, because being in the pipe wall it should be very 

 free from induction, because the air velocity is so much 

 lower there ; secondly, because it was strongly recom- 

 mended to the author by Mr. S. C. Davidson, of Belfast, 

 who has done much good work in this direction. 



The Nipher collector (Fig: 2) is a disc gauge made up 

 of a number of discs of gauze held between two plates. 

 The air passing into the central tube a (Fig. 2) must 

 pass through the holes h in the outer disc and thence 

 through the gauze. The Brabbee tube will be seen from 

 Fig. 3 to consist of a side gauge, combined with a facing 

 gauge. Pressure readings are taken from the pipe a, 

 which is in communication with the holes//. Ifthepartof 

 the tube containing the holes // is parallel with the air duct 



