Källén writes on his recent attempts to simplify the calculations on quantum electrodynamics.

Källén talks about calculation on an integral-representation of the S$_{c}$-function, avoiding the complex method of integration.

Källén encloses a manuscript dealing with the contents of his last letter of the 12 December 1949, in addition to a calculation on bosons in an external field.

Källén talks about some general observations on the mathematical formalism of the Lee model.

Nilsson reinterprets Rydberg's "triplets". He gives a modern level scheme.

Nilsson reports on Siegbahn's response to Pauli's inquiries about Rydberg's new elements of 1913.

Nilsson encloses a photo of J R Rydberg.

Nilsson makes remarks on Rydberg's 1913 postulate of two new elements. He talks about the "wechselsatz' multiplet.