126 JOHN BERRY HAYCRAFT ON 
A dotted line in Chart represents what would occur were the population 
stationary. It is now seen that when these two disturbing factors are discarded, 
that the two curves present a most striking contrast. There are two maxima 
in each, 
The smaller marriage maximum in December and January is followed by 
the smaller conception maximum in about two months,—this can be seen from 
this Chart, but will be proved from FourteEr’s curves. 
The larger marriage crest in June and July is followed in the same interval 
by the larger conception crest. 
It will be seen that directly after a marriage rise a conception increase also 
takes place, thus the rise from May to June in the marriages is followed directly 
by a rise in the conceptions. This is as might be expected; they go on increas- 
ing until a maximum is reached in the second month, when most occur, The 
numbers then diminish, falling to a minimum. 
By Fourier’s curves the interval between marriage and time of maximum 
of conceptions is almost exactly two months. 
This point, which is of some interest from both a physiological and statistical 
view, is brought out, namely, that most conceptions do not take place for some 
time after marriage,—not until, in fact, after an interval of two months; and 
that therefore most children are born eleven months after marriage. 
This has been already variously stated, and the interval quoted varies from 
10°5 (SADLER) to 17 (M. Duncan) months. 
For the results here given it may be claimed that by far the largest data 
ever used were brought to bear upon the subject (not being a mere tabulation 
of cases); and that the use of FourRIEr’s analysis gives an exactitude not 
otherwise attainable. 
Yet another point may be mentioned: by comparing the altitudes of the 
curves, it will be seen that an increase of 100 marriages on the average produces 
an increase of sixty-four conceptions within a period of five months. 
Stated otherwise, sixty-four per cent. of newly-married women have a child 
within a period of fourteen months. 
This latter fact must, however, be received with a certain caution, as the first 
births are mixed up with the second, third, and so on; and although the first 
births will give the chief character to the curve, and the phase will not be 
vitiated, yet the altitude cannot be taken as quite correct. | 
From these curves a very important series of investigations can be made. 
The ‘duration of pregnancy” can be arrived at, a result thought before impos- 
sible ; and also the interval between “insemination” and “ conception.” 
The results which are before the Society to-night must not on this point be 
considered final, merely the “‘method of inquiry” will be indicated, and its 
application to the above curves will be made. 
