EINSTEIN, Albert (1879-1955)
EINSTEIN, Albert (1879-1955)
EINSTEIN, Albert (1879-1955)
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EINSTEIN, Albert (1879-1955)

Autograph letter signed ('A. Einstein') to [Wander and Geertruida] de Haas ('Meine lieben De-Haasen!'), n.p. [Berlin], n.d. [before 15 November 1915].

Details
EINSTEIN, Albert (1879-1955)
Autograph letter signed ('A. Einstein') to [Wander and Geertruida] de Haas ('Meine lieben De-Haasen!'), n.p. [Berlin], n.d. [before 15 November 1915].
In German. 21⁄4 pages, 223 x 143mm, on a bifolium, annotation in pen, 'Herbst 1915', to upper margin of f.1r and blank verso of f.2. Provenance: Sotheby's, 5 December 1996, lot 197 (part) – Christie's, 8 June 2005, lot 104.

On the equivalence principle, magnetism and the Einstein-de Haas experiment, written while Einstein was finalising the general theory of relativity. In a letter of rich scientific content, written at one of the summits of Einstein's scientific career, he refers to the confirmation of the equivalence principle ('the negative result of the independence of gravitational acceleration from matter'), his investigations into the causes of magnetism including the Einstein-de Haas effect, and his admiration for his hero, James Clerk Maxwell ('what a nose that man had!').

'With gravitation there is, as far as I can see, not much to be done in the laboratory. The negative result of the independence of gravitational acceleration from matter has probably been demonstrated sufficiently enough. It would suffice for me, even if there were no experiments at all with radioactive materials. In the end these materials, since we can observe their transformations, will not show any unusual inertial behaviour.

I am very much looking forward to your paper on the effect. I have also conducted experiments in which I reversed the remnant magnetism through the discharge current of a condenser. The thing has however up to now not succeeded, since in spite of the short duration of the field (103"), a strong vibration of the rod ensued, which covered up the effect. This will naturally be avoided in your method. I hardly believe that your 10% difference with the theory is real. But if it were so, it would be very important. I actually still do not know what Maxwell has done on the subject. In any case, it is again clear here what a nose that man had! ...'

Einstein goes on to refer to de Haas's work with metal electrons, and congratulates him on a lathe he had devised: 'the thing has style'. The letter opens with a delighted reaction to an 'exquisite' letter from the de Haases, and congratulations on Wander de Haas's decision to switch from research in Berlin to schoolteaching in the Netherlands: 'teaching is very amusing, and especially if one is facing solid, unspoiled country children with healthy nerves. I think that I too could still find myself in a similar position with enjoyment'.

The Equivalence Principle lies at the heart of general relativity: the equivalence of gravitational and inertial mass is the key concept differentiating special relativity from general relativity. As Einstein recounted in a 1920 essay, he was reflecting on the challenge of integrating gravity into special relativity in 1907 when he had 'the happiest thought of my life': that a person releasing an object while himself falling downward from a roof will not be able to detect the effects of gravity on the object (this 'happiest thought' is now often expressed in the context of an elevator in free fall in a gravitational field.) The principle, however, was not new with Einstein: Isaac Newton himself conducted experiments seeking to substantiate the principle, and other scientists after him, with the principle only finally being considered empirically proven by the experiments of Lorand Eotvos at the end of the 19th century. Einstein here states that, in his view the Equivalence Principle 'has probably been demonstrated sufficiently enough' by such experiments – even without the confirmatory evidence provided by Wilhelm Wien’s 1912 experiments with radioactive materials ('It would suffice for me, even if there were no experiments at all with radioactive materials'). Internal evidence within the letter points to a dating immediately before the November 1915 publication of the general theory of relativity (in four ground-breaking papers presented to the Prussian Academy of Sciences). It is very striking that at this late stage of the process – on the verge of publishing his field equations for gravitation – Einstein is still thinking about the need to reinforce the very pillar on which General Relativity was built.

The discussions of magnetism in the letter relate to what is known as the Einstein-de Haas effect, after their joint paper, published in April 1915, in which they demonstrated experimentally the phenomenon by which a change in the magnetic motion of a body causes it to rotate. It has been referred to as 'the only experiment of Einstein's career', and crucially demonstrated what actually causes magnetisation. The forthcoming paper to which Einstein refers was de Haas's follow-up experiments on molecular currents (published 18 October). Einstein's own experiments on remnant magnetism were published in a report presented to the Deutsche Physikalische Gesellschaft on 25 February 1916 (Einstein 1916d): the problems of which he complains were caused by an eccentricity in the suspension of the bar. The reference to James Clerk Maxwell is also significant: Maxwell was, perhaps even more than Newton, Einstein's scientific hero, and the inspiration for relativity.

The Dutch physicist Wander de Haas (1878-1960) had spent four years in Berlin, latterly at the Physikalish-Technische Reichanstalt, where he collaborated with Einstein. At the time of the present letter he had recently returned to the Netherlands to teach at a secondary school in Deventer; in 1917 he was appointed as professor of physics at Delft, and subsequently at Groningen and Leiden. Einstein's reference to the attractions of school-teaching is amusing: his only experience as a teacher had been 1901, after his graduation from Zurich Polytechnic.
Special notice

This lot has been imported from outside of the UK for sale and placed under the Temporary Admission regime. Import VAT is payable at 5% on the hammer price. VAT at 20% will be added to the buyer’s premium but will not be shown separately on our invoice.

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Julian Wilson
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