Morley and Brush — Measurement of Small Pressures. 455 



Art. XXXVIII. — A new Gauge for the Measurement of Small 

 Pressures; by Edward W. Morley and Charles F. 

 Brush. 



In 1888 and again in 1889, one of ns constructed two 

 gauges of a new form, intended for the direct measurement 

 of small pressures. About three years ago, a third instrument 

 of the same kind was used by us for the measurement of the 

 pressure of the vapor of water ; the time required for a 

 measurement was rather long, and we accordingly constructed 

 two more instruments of a somewhat different form, in which 



the time needed for a reading is no more than that required 

 by a filar micrometer. We shall now describe both forms ; 

 not only the somewhat costly apparatus which economizes 

 time when many measurements are to be made, but also the 

 simple and less expensive form which may well serve where 

 but few measurements are required. 



In figure 1, a h is a siphon gauge, consisting of tubes about 

 five centimeters in diameter, connected below by a smaller 



