362 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
the value of A is found as 
A =0.40 
This figure is of the same order of magnitude as the 0.316 
found in § 333-6. Here again, the divergence can be attributed 
‘0 the approximative nature of the hypothesis (H”), on the 
assumption that the exponential model is valid. But if this 
approximation is admitted, the concordance of orders of magni- 
tude indicates that, if hypothesis (H"”) is taken to be approxim- 
ately true, the exponential model can be considered as not 
departing very far from reality. 
This reasoning shows, at least intuitively, how the assump- 
tion of exponential amortization of primary income is justified. 
If the general formulation of the exponential model is taken 
as exact, it also supplies an estimate of the order of magnitude 
of the proportion A of primary income incorporated in invest- 
ment, which agrees with observed data (1). 
(!) Of course it would be of the greatest possible interest to generalise 
‘he above reasoning to the case in which the lengths of the production 
ind amortisation periods of different types of investment are no longer 
considered as uniform, but the frequency of a production period extending 
irom § to 6+ df would be (6) de, and the frequency of an amortisation 
period for primary inputs extending from 6 to 0+d6 would be ¢(6)d6, 
with the discrete model becoming continuous (See § 333-2 above). Up to 
now, I have been unsuccessful in making a calculation of this kind. If it 
could be done, it would doubtless enable the validity of the exponential 
model to be verified efficiently, by determining the relations between the 
quantities A, x and @ and the data Rc, C et p, using this model. 
In present circumstances, and in the absence of a calculation of this 
kind progress can onlv be made on the basis of rough estimates 
11] Allais - pag. 166