Letter of uncle Dolf of 22 August 1920 in which he invited his cousin:
.. I don’t want to push you Harm but as I’ve always said, one knows what the world offers after he has seen the world. If you like, if you really want to, I hope you will be my guest during your journey, for me it will be a great pleasure to show you the world…(p.13)

Dolf Kamerlingh Onnes

Dolf Kamerlingh Onnes