EINSTEIN'S COLLABORATORS 493ham Flexner, the first director of the Institute, Einstein insisted on an appoint-
ment for Mayer as an essential condition for his own acceptance of the new posi-
tion. After other conditions of his professorship had been settled to mutual
satisfaction, Einstein wrote to Flexner, 'Now my only wish is that Herr Dr W.
Mayer, my excellent co-worker, will receive an appointment that is formally inde-
pendent of my own. Until now, he has suffered very much from the fact that his
abilities and achievements have not found their deserved recognition. He must be
made to feel that he is being appointed because of his own achievements and not
for my sake' [E39].
The next two Einstein-Mayer papers again dealt with semi-vectors [E40,
E41]. They were produced during their stay at Le Coq sur Mer in Belgium (see
Section 25b). At that time, the spring of 1933, Mayer's Princeton appointment
had still not been settled, and Einstein wrote to Flexner urging him to exercise
care in the choice of people he might approach for opinions on Mayer [E42]. A
subsequent letter to Flexner shows that Einstein could put the pressure on if he
wanted to: 'You will by now have learned through the press that I have accepted
a chair at Madrid University. ... In view of my relations to the Spanish govern-
ment, I feel it is my duty to write to you about my assistant, Professor W. Mayer.
The Spanish government has conceded me the right to recommend to them a
mathematician to be appointed as full professor under my direction. Now, as I
have very great regard for Professor Mayer's abilities, not only as my collaborator
but also as an independent researcher in pure mathematics whose achievements
are notable and valuable, he would be the right man to take up such a professor-
ship. He would not have thought of asking me to recommend him for this post
had he not felt it as a set-back that he was appointed to your Institute not as a
full professor but only as an associate professor with a salary that hardly corre-
sponds to his merits and his needs. I therefore find myself in a difficult position:
either to recommend him for Spain or to ask you whether you could possibly
extend his appointment to a full professorship. This would be the only way of
retaining him for your Institute and for a collaboration with me. I would deplore
it very much indeed if I were deprived of his valuable collaboration; and his
absence from the Institute might even create some difficulties for my own work.
Besides, his resignation would be a great loss to your Institute' [E43].
The very high importance which Einstein still attached to the collaboration
with Mayer is also evident from his reply to a proposal by Flexner that Mayer
arrive in Princeton some weeks before Einstein would be there: '[This] would
severely impair our joint work. .. [since] we would be torn away from each other
[voneinander gerissen] for a whole month .. .' [E44].
Einstein prevailed, and Mayer was given a tenured position with the title of
associate, the only appointment of its kind ever made by the Institute. The entire
collaboration of Einstein and Mayer in the United States consists of one joint
paper, the last one on semi-vectors [E45]. After 1934 Mayer returned to his own
pursuits in pure mathematics. It is my understanding that he no longer wished to