Note on a simple form of Lippmann's capillary electrometer useful to physiologists / by Professor John G. M'Kendrick, M.D.

  • McKendrick, John G. (John Gray), 1841-1926.
Date:
[1883?]
Catalogue details

Licence: Public Domain Mark

Credit: Note on a simple form of Lippmann's capillary electrometer useful to physiologists / by Professor John G. M'Kendrick, M.D. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    T 348 lippmann’s capillary electrometer. column of mercury will not always return to. zero when the electro-motive force pushing it in one direction has ceased to act. When it does return, the return is due to the pressure of the column of mercury against which the force acted. As a matter of fact, the most sensitive instruments are those which do not return to zero, but in which the movement of the mercurial column corresponds to each change in the direction of the electro- motive force, or to any increase or diminution of the electro- motive force eveD in one direction. Thus, if there be a negative oscillation, it will be at once seen, although it last for a fraction of a second. Sometimes the instrument is “ sluggish ” in its movements. This is caused by the mercury, or the acid, or the tube not being perfectly clean. An electrometer such as this can have its deflections photo- graphed1 or exhibited on a screen, whilst its simplicity and cheapness makes it possible to place a sensitive instrument in the hands of every student—or, better still, a student may make it for himself.2 Tor convenience in working, when it may be necessary to make observations with a galvanometer at the same time, the image of the capillary may be thrown on the plate of a camera, adjusted to a microscope, and thus the trouble of looking through the latter is got rid of. 1 Marey obtained such a photograph in his research on the Electrical Discharge of the Torpedo (Physiologie Experimentale, 1877, p. 33, fig. 19), and Burdon Sanderson has photographed the oscillations caused by the changes of potential in Dionsea, and in the frog’s heart.—Royal Institution Lecture, fig. 10. 2 Various forms of the instrument were shown, and the oscillations of the mercury were projected on a screen, the oscillations being magnified 300 diameters. There is nothing novel either in the theory or in the mechanism of this instru- ment, as it in no way differs in principle from one shown at the meeting of the British Association in Glasgow in 1876, by Professor Dewar of Cambridge, but I have shown an easy and convenient mode of making such an instrument of exquisite delicacy for physiological purposes. A figure of Professor Dewar’s instrument is shown in Dr. S P. Thompson’s recent Manual on Electricity.