The London, Edinburgh and Dublin philosophical magazine and journal of science . ctromotive forces which occur in the pneumatic keysdescribed are much too small to produce an observable effectupon the readings of the most sensitive capillary electro-meter*. The sensitiveness of the electrometer, using the simple keyfirst described, is such that when the diameter of the widetubes is about 1 cm. and the diameter of the capillary isabout 1 mm., a movement of the meniscus perceptible withcertainty in a microscope magnifying 100 times is producedby a potential-difference equal to 0001 volt. The act
The London, Edinburgh and Dublin philosophical magazine and journal of science . ctromotive forces which occur in the pneumatic keysdescribed are much too small to produce an observable effectupon the readings of the most sensitive capillary electro-meter*. The sensitiveness of the electrometer, using the simple keyfirst described, is such that when the diameter of the widetubes is about 1 cm. and the diameter of the capillary isabout 1 mm., a movement of the meniscus perceptible withcertainty in a microscope magnifying 100 times is producedby a potential-difference equal to 0001 volt. The actualextent of the movement is somewhat variable, and amountsusually to about *01 mm. The follov/ing numbers, obtainedwith apparatus previously described (Phil. Trans. A. 189y,vol. cxciii. p. 63), show the effect of comparatively large * Since this paper was read I have found that mercury keys (similarin principle to those referred to above) in which the thermoelectriceffects are reduced to a minimum are described by Kamerlingh Onnes,Ley den Communications, No. 27, p. 31, Portable Capillary Electrometer. 403 polarizing electromotive forces upon the surface-tension be-tween mercury and sulphuric acid solution of density 1*17 :— Volts. Surface-Tension. 0 y 0-0202 1-021 7 0-0404 1-040 y 0-0605 1-059 7 0-0807 1-080 y 0-1009 1-097 y 7 is the natural surface-tension between the mercury andthe solution. Its approximate value is 300 ergs per sq. from these numbers, it would seem that the surface-tension is altered by about one part in 10,000 by a of -0001 volt. In the case in which the capillary-tube is horizontal and the wide tubes are vertical, the relationbetween the motion of the meniscus 8a and the correspondingchange in surface-tension By is expressed approximately by c?p g hx=KcByif we assume that the capillary and wide tubes are of uniformcross-section—a being the area of cross-section of the capil-lary, a its circumference, A the area
Size: 1146px × 2180px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1840, bookidlondon, booksubjectscience
