JF Ptak Science Books *Quick Post*

I bumped in this issue of *Nature* (volume 106**,** pp782–784) this evening, and as it turns out it is the "Special Number: Relativity" and published February 17, 1921--and it is packed. Somehow when I first looked at this weekly I mega-missed the Einstein entry--as is customary I work back-to-front, bottom-to-top (don't ask) and was so taken by the collection of Big Names that Einstein's escaped me. Einstein's article is longish for this journal and concise, with numerous references in the influencing forces in his development of the theory of relativity (which he capitalizes).

The table of contents for this single week--though it is (roughly) a double issue of thirty pages or so--incoudes work by Cunningham, Frank Dyson, James Jeans, H.A. Lorentz, Oliver Lodge, Herman Weyl, A.S. Eddington, Norman Campbell, and Harold Jeffreys, plus a few pages of tight bibliography.

Here's the beginning of the Einstein article, courtesy of *Nature*, with the rest of it available from their website, here. My copy (formerly in the Smithsonian Institution) is too tender to open fully for the scanner, but the cover's masthead is certainly available, and pretty. Abraham Pais notes in his *Subtle is the Lord : The Science and the Life of Albert Einstein, *that Einstein delayed the publication of the issue somewhat in his attempts to make a complicated issue fit in the space allot (as in the old Mark Twain adage, "If I had more time I would have written a shorter letter"). So, the Einstein:

*A Brief Outline of the Development of the Theory of Relativity,* by Prof. A. Einstein

[Translated by Dr. Robert W. Lawson]

There is something attractive in presenting the evolution of a sequence of ideas in as brief a form as possible, and yet with a completeness sufficient to preserve throughout the continuity of development. We shall endeavour to do this for the Theory of Relativity, and to show that the whole ascent is composed of small, almost self-evident steps of thought.

The entire development starts off from, and is dominated by, the idea of Faraday and Maxwell, according to which all physical processes involve a continuity of action (as opposed to action at a distance), or, in the language of mathematics, they are expressed by partial differential equations. Maxwell succeeded in doing this for electro-magnetic processes in bodies at rest by means of the conception of the magnetic effect of the vacuum-displacement-current, together with the postulate of the identity of the nature of electro-dynamic fields produced by induction, and the electro-static field.

The extension of electro-dynamics to the case of moving bodies fell to the lot of Maxwell's successors. H. Hertz attempted to solve the problem by ascribing to empty space (the æther) quite similar physical properties to those possessed by ponderable matter; in particular, like ponderable matter, the æther ought to have at every point a definite velocity. As in bodies at rest, electro-magnetic or magneto-electric induction ought to be determined by the rate of change of the electric or magnetic flow respectively, provided that these velocities of alteration are referred to surface elements moving with the body. But the theory of Hertz was opposed to the fundamental experiment of Fizeau on the propagation of light in flowing liquids. The most obvious extension of Maxwell's theory to the case of moving bodies was incompatible with the results of experiment.

At this point, H. A. Lorentz came to the rescue. In view of his unqualified adherence to the atomic theory of matter, Lorentz felt unable to regard the latter as the seat of continuous electro-magnetic fields. He thus conceived of these fields as being conditions of the æther, which was regarded as continuous. Lorentz considered the æther to be intrinsically independent of matter, both from a mechanical and a physical point of view. The æther did not take part in the motions of matter, and a reciprocity between æther and matter could be assumed only in so far as the latter was considered to be the carrier of attached electrical charges. The great value of the theory of Lorentz lay in the fact that the entire electro-dynamics of bodies at rest and of bodies in motion was led back to Maxwell's equations of empty space. Not only did this theory surpass that of Hertz from the point of view of method, but with its aid H. A. Lorentz was also pre-eminently successful in explaining the experimental facts.

Continued at the *Nature* site, here.

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