While Giblin was delivering his lecture, the Cambridge version of the multiplier was still more than a year from publication (in the June 1931 issue of the Economic Journal). Indeed it was not even yet formulated. It was to be conceived by Keynes’ star pupil, Richard Kahn, during mid-1930, while on a walking holiday in the Austrian Alps.

Giblin’s version of the multiplier is indubitably prior. Although this is recognised, Giblin’s multiplier is largely ignored in the historiography of Keynes’ General theory. Patinkin (1993) never mentions Giblin is his chronology of the General theory. Giblin’s multiplier is referred to only once in Skidelsky’s biography of Keynes – and only by implication, and only in a footnote.^[16] And there is a good reason for this silence: neither Keynes, nor Kahn, nor any ‘Circus’ members ever mention Giblin’s multiplier. There is no positive evidence that any of these people read it.^[17] In fact, there is some positive evidence that they did not read it. First, not long after Keynes began using multiplier analysis in 1933, Giblin wrote that, in doing so, Keynes was following Kahn, rather than himself.^[18] Secondly, Keynes baldly states in the General theory:

Yet, on account of his Cambridge associations, it is intellectually legitimate to consider that Keynes and his circle were aware of the Giblin multiplier. And it is intellectually legitimate to be tantalised by the fact that King’s College library does contain a copy of Australia, 1930. Giblin sent it to them. It arrived in June 1930.^[20] Nevertheless, there is no positive evidence that Keynes or any of his circle read, or were aware, of Giblin’s multiplier.^[21] The two multipliers were ‘doubletons’.

A simultaneous but independent formulation of the multiplier is made more likely by the fact that two other economists, in languages other than English, advanced the concept (apparently independently): Jens Warming in 1929–30, and Michal Kalecki in 1933 (see King 1998). The following table compares the various multipliers.