Prof. Fowler expressed regret at the absence of Messrs Babcock, Burns, Kayser and Nagaoka.

In opening the discussion on sources of the primary standard, Prof. Fowler presented the following extracts from a communication which had been forwarded by Mr Babcock:

“The preliminary specifications adopted by the I.A.U. in 1925 are a simplified description of the Michelson lamp, naming the conditions which were at that time considered necessary and sufficient by Prof. Fabry himself. Even by implication they do not suggest a substitute for the original lamp. It goes without saying that a vacuum tube provided with internal electrodes is not intended for use with high frequency, but rather with the customary well-known type of excitation. In any case, before amending our specifications so as to prohibit high frequency excitation, at least three laboratories should agree that this is necessary.”