788. Harrod to J. Marschak , 5 July 1938 [a] , 
[The exchange continues at 800 ]
Ch[rist]. Ch[urch, Oxford].
5 July 1938
My dear Marschak
I do hope the operation went off successfully and that you are now well on the way to recovery.
In the course of the last year I have been thinking a good deal about the "dynamic" theory propounded in my last book  and I have now got it (in my head) into much better shape.  I feel that this latest construction really should carry conviction.
But I feel also that I really ought to do a little experimenting with figures. At this I am quite unpracticed; and I should immensely value it, if you feel you can spare the time and attention, to have a discussion about ways and means of verification and development by reference to statistical materials. If I were set down in your Institute  to-morrow I should be quite at a loss how to proceed. But after some discussions of the points at issue with you I might see my way more clearly.
Meanwhile past experience has shown only too well that the amount of time available to me is all too limited. I wonder whether after I have made certain beginnings on my own account we might set one of our young men onto doing some of the further work required?
I notice that Tinbergen has been throwing some doubt on the acceleration principle.  But my theory as now stated accounts for the Trade Cycle at least as much in terms of deviation from it as in terms of it. Not that I have any absolutely rigid theory. But I believe I have a structure of concepts which would make a good starting point.
I am going away for a fortnight partly on pleasure but also to a conference in Cambridge on Tinbergen's work.  Then from July 20 until the British Ass[ociation] I shall be at Uffington (within reach of Oxford). During that time I should hope to get my stuff written up. When it is typed I should very much like to send you a copy for you to peruse at your leisure before we start talking. We might have a preliminary talk either here during my Uffington period, if you happen to be here, or in Cambridge at the time of the British Ass. I hope all this is not proposing too big an encroachment on your time!
2. Harrod, The Trade Cycle ( 1936:8 ).
3. Harrod later recollected that he "suddenly saw [his `growth equation'] in a split second", "not in [his] Oxford study, but in John Betjeman's cottage in Berkshire, which he lent [him] in July 1938" (Harrod, Economic Dynamics, London: Macmillan, 1973, p. 41). This passage, which in conjunction with the urge to proclaim his discovery to Robertson (letter 789 , [jump to page] , written on the same day) and to Keynes (letter 790 , [jump to page] , written on the following day) seems to confirm the impression of suddenness, disproves the statement regarding Betjeman's cottage, where Harrod stayed from 20 July to 11 August 1938 (see source note b to letter 798 ). The re-shaped dynamic theory, however, was written up in Berkshire: Harrod finished drafting it on 3 August, and submitted it to Keynes for publication in the Economic Journal on 6 August as "An Essay in Dynamic Theory": the draft is reproduced here as essay 19 (see note 1 for a more detailed chronology and references to the preliminary discussions with Keynes and Marschak), the final version appeared in March 1939 (Harrod 1939:7 ).
4. The Oxford Institute of Statistics, of which Marschak was the Director.
5. Harrod probably refers to J. Tinbergen, "Statistical Evidence on the Acceleration Principle", Economica V, May 1938, pp. 164-76. Although he had already received a draft of Tinbergen's Statistical Testing of Business Cycle Theories (1939), where the acceleration principle is also discussed (see, in particular, part I, p. 39), Harrod only read it later: see letter 789 , [jump to page] .
6. Harrod was invited by Loveday to participate in a "small meeting of experts" for a discussion of Tinbergen's League of Nations reports, to be held in Cambridge from 18 to 20 or 21 July 1938: see letter 772 .
- a. ALS, two pages on two leaves, in JMP 1275, Box 147, folder H.
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