Letter | Published:

Dimensions of Fundamental Units

Nature volume 131, page 585 (22 April 1933) | Download Citation



PROF. CRAMP has proposed1 that the dimensional expressions for the electrostatic and electromagnetic units may be simplified by regarding quantity of electricity Q as fundamental. To my reply2, that including Q would cause confusion because, whereas M, L and T are quantities which vary with the velocity of the observer, Q is invariant, Prof. Cramp's2 rejoinder is the question: How it is known that Q is invariant? The invariance of the charge carried by a moving particle is, I believe, generally accepted. A simple proof of the consistency of this invariance with the special principle of relativity is given in N. R. Campbell's “Modern Electrical Theory”, p. 361.

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  1. 1.

    NATURE, 130, 368, Sept. 3, 1932.

  2. 2.

    NATURE, 130, 892, Dec. 10, 1932.

  3. 3.

    NATURE, 131, 59, Jan. 14, 1933.

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  1. Department of Electrical Engineering, University of New Mexico, Albuquerque. Feb. 12.

    • F. M. DENTON


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