Units of Pressure in Vacuum Work

Abstract

REFERRING to the letter by Mr. Shaw in NATURE of March 20 (p. 95), I beg leave to remind readers that we have already a convenient unit of pressure which, as fitting in an absolute system of units, is preferable to the micron of mercury, viz. the dyne per cm.², or the barye of the c.g.s.-system. In fact, Prof. Knudsen has used it in all his later researches on molecular phenomena. In article V10 of the “Encyklopaedie der mathematischen Wissenschaften,” p. 628, note 19, (Communications from the Physical Laboratory at Leyden, Suppl. No. 23, p. 14), by Prof. Kamerlingh Onnes and myself, we have given practically the same unit under the name of millitor as convenient for such pressures as those in Röntgen vacua.