5.  Gratifying, however, though this irregularity of the curve may be, yet it entails a corresponding disadvantage, for we are precluded thereby from readily perceiving the characteristics of the monthly rhythm as a whole.  I thought that perhaps this aspect of the rhythm might be rendered plainer if I calculated the data into two-day averages; and the result, as shown in Chart 10, is extremely satisfactory.  Here we can at once perceive the wonderful and almost geometric symmetry of the monthly rhythm; indeed, if the third maximum were one unit higher, if the first minimum were one unit lower, and if the lines joining the second minimum and third maximum, and the fourth maximum and fourth minimum, were straight instead of being slightly broken, then the curve would, in its chief features, be geometrically symmetrical; and this symmetry appears to me to afford a convincing proof of the representative accuracy of the curve.  We see that the month is divided into five periods; that the maxima occur on the following pairs of days:  the 19th-20th, 13th-14th, 25th-26th, 1st-2d, 7th-8th; and that the minima occur at the beginning, end, and exact middle of the month.  There have been many idle superstitions as to the influence of the moon upon the earth and its inhabitants, and some beliefs that—­once deemed equally idle—­have now been re-instated in the regard of science; but it would certainly seem to be a very fascinating and very curious fact if the influence of the moon upon men should be such as to regulate the spontaneous discharges of their sexual system.  Certainly the lovers of all ages would then have “builded better than they knew,” when they reared altars of devotional verse to that chaste goddess Artemis.

THE WEEKLY RHYTHM.

We now come to the third branch of our inquiry, and have to ask whether there be any weekly rhythm of the sexual activity. A priori it might be answered that to expect any such weekly rhythm were absurd, seeing that our week—­unlike the lunar month of the year—­is a purely artificial and conventional period; while, on the other hand, it might be retorted that the existence of an induced weekly periodicity is quite conceivable, such periodicity being induced by the habitual difference between our occupation, or mode of life, on one or two days of the week and that on the remaining days.  In such an inquiry, however, a priori argument is futile, as the question can be answered only by an induction from observations, and the curves on Chart 11 (A and B) prove conclusively that there is a notable weekly rhythm.  The existence of this weekly rhythm being granted, it would naturally be assumed that either the maximum or the minimum would regularly occur on Saturday or Sunday; but an examination of the curves discloses the unexpected result that the day of maximum discharge varies from year to year.  Thus it is[383]