282 RELATIVITY, THE GENERAL THEORY- Einstein and Mach. Einstein was in the middle of preparing his first synopsis
on general relativity when in February 1916 word reached him that the sufferings
of Mach had come to an end. He interrupted his work and prepared a short article
on Mach [E26] which reached the editors of Naturwissenschaften a week before
his synopsis was received by the Annalen der Physik. The paper on Mach is not
just a standard obituary. It is the first occasion on which Einstein shows his excep-
tional talent for drawing with sensitivity a portrait of a man and his work, placing
him in his time and speaking of his achievements and of his frailties with equal
grace.
Mach was successively a professor of mathematics, experimental physics, and
philosophy. In the obituary, Einstein lauded a number of diverse contributions
but reserved his highest praise for Mach's historical and critical analysis of
mechanics [M6], a work that had profoundly influenced him since his student
days [E27], when he was introduced to it by Besso [E28]. He had studied it again
in Bern, together with his colleagues of the Akademie Olympia [Sll]. In 1909 he
had written to Mach that of all his writings, he admired this book the most
[E29].* Initially, Mach seems to have looked with favor on relativity, for Einstein
wrote to him, again in 1909, 'I am very pleased that you enjoy the relativity theory'
[E30]. In the obituary, Einstein cited extensively Mach's famous critique of New-
ton's concepts of absolute space and absolute motion and concluded, 'The cited
places show that Mach clearly recognized the weak sides of classical mechanics
and that he was not far from demanding a general theory of relativity, and that
nearly half a century ago!' [E26]. In his nineteenth century classic, Mach had
indeed criticized the Newtonian view that one can distinguish between absolute
and relative rotation. 'I cannot share this view. For me, only relative motions exist,
and I can see, in this regard, no distinction between rotation and translation,' he
had written [M7].** Einstein had Mach's discussion of rotational motion in mind
when he wrote his own 1916 synopsis: its second section, entitled 'On the Grounds
Which Make Plausible an Extension of the [Special] Relativity Postulate,' begins
with the phrase:
Classical mechanics, and the special theory of relativity not less, suffer from an
epistemological shortcoming [the preferred position of uniform translation over
all other types of relative motion] which was probably emphasized for the first
time by Mach. [E6]
In 1910, Mach had expressed himself positively about the work of Lorentz,
Einstein, and Minkowski [M8]. Around January 1913, Einstein had written to
him how pleased he was with Mach's 'friendly interest which you manifest for
*Four letters from Einstein to Mach have been preserved, none from Mach to Einstein. These letters
are discussed in essays by Herneck [H9] and by Holton [H10], along with more details on the
relations between the two men.
**In this connection, readers may wish to refresh their memory about Newton's rotating bucket
experiment and Mach's analysis thereof; see, e.g., [W18]. In February 1916, Einstein gave a lecture
on the Foucault pendulum [E31].