Medical electricity / By H. L. Jones ... Being the third edition of Medical Electricity, by W. E. Steavenson, M.D., and H. L. Jones, etc.

  • Steavenson, W. E. (William Edward), 1850-1891.
Date:
1900
Catalogue details

Licence: In copyright

Credit: Medical electricity / By H. L. Jones ... Being the third edition of Medical Electricity, by W. E. Steavenson, M.D., and H. L. Jones, etc. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    quotation from Clerk Maxwell to give some idea of the meaning of the word, but the student who wishes to obtain a thorough insight into it cannot do better than read Clerk Maxwell's Elementary T/eaiise on Electricity, giving special attention to Chapter III,, on Electrical Work and Energy. In most of what follows, and es- pecially in the part which refers to electricity in motion, the idea of electric pressure in connection with the word potential will be the dominant one ; but it must always be remembered that this idea of pressure is based on the analogy of the electric flow to a fluid flow, and this is at best very imperfect. 15. Electrometers.—The only thing that can be observed in connection with electricity at rest is a difference of potential. It is possible to measure the quantity of electricity driven through certain instru- ments, just in the way that a quantity of water driven through a water meter can be measured, and some of these instruments will be discussed in a future chapter; but for the present we can only appreciate electrical charge by observing a difl'erence of potential, and elec- troscopes and electrometers are instruments for showing or measuring differences of potential. The gold leaf electroscope has been shortly referred to above. The divergence of the leaves of this instru- ment may be taken as an indication that the knob or disc, or way by which electricity enters the instrument, is at a different potential to the walls of the room, or to that of the metal cage that surrounds some forms of the instrument, but obviously without further observation it does not tell whether the potential is higher or lower, i.e., more positive or more negative, and further tests must be made to discover this. Neither does it give us more than the roughest indication of the amount of