Blair's recent theory of excitation is analysed with the following conclusions:
1. The theory is inapplicable to currents of long duration; i.e., slowly increasing currents and the opening excitation.
2. The theory is a modification of the condenser theory of excitation but the modification is to be rejected on three grounds:
(a) The modification has no obvious physical significance.
(b) It does not in fact remedy the divergence between calculation and observation.
(c) It leads to certain conclusions of a surprising kind which are contrary to observed fact.
3. The qualitative value of the condenser theory is demonstrated by the fairly close agreement between calculation and observation over a considerable field of enquiry.