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It is important to note that tendencies (ii) and (iv) are transitory, and that as long as they operate the rates of invention and the resultant productivity changes are higher than they will be once the transition is over. It follows that the small size of the R&D sector and the large time-lags between inventions and first applications at the beginning of the industrial revolution have been a reserve of faster productivity change later on. This is a finite reserve and, judging from Figures 3.1 and 3.2 with reference to (iv), the world may be near to its full exploitation. Another such reserve at the world economy level is the low application rate for a large number of modern inventions in less-and medium-developed countries - the part of the world behind the TFA. Later in the book we shall study the implications of the latter reserve as well as of tendencies (ii) and (iv) for the innovation rate and the growth of conventional output.