This law it is possible to represent graphically as a curved line; a succession of crests and hollows as in all wave-lines. Its simplest and most fundamental expression, however, is generally immensely complicated by other stimulations which may bring into it diverse series of waves, or irregular wave-crests. We have all, at some time, watched the regular ripples of the sea breaking against a sand-bank, and noticed that the influx of another current of water may send a second system of waves at right angles to the first, cutting athwart them, so that the two series of waves pass through each other.
Woman is so sensitive and responsive an instrument, and so liable in our modern civilised world to be influenced by innumerable sets of stimuli, that it is perhaps scarcely surprising that the deep, underlying waves of her primitive sex-tides have been obscured, and entangled so that their regular sequence has been masked in the choppy turmoil of her sea, and their existence has been largely unsuspected, and apparently quite unstudied.
For some years I have been making as scientific and detailed a study as possible of this extremely complex problem. Owing to the frank and scientific attitude of a number of women, and the ready and intimate confidence of many more, I have obtained a number of most interesting facts from which I think it is already possible to deduce a generalisation which is illuminating, and may be of great medical and sociological value. A detailed statement of this will be given in a scientific publication, but as it bears very intimately on the subject of the present chapter, a short and simple account of my conclusions must be given here.
It is first necessary to consider several other features of woman's life, however.
The obvious moon-month rhythm in woman, so obvious that it _cannot_ be overlooked, has been partially studied in its relation to some of the ordinary functions of her life. Experiments have been made to show its influence on the rate of breathing, the muscular strength, the temperature, the keenness of sight, etc., and these results have even been brought together and pictured in a single curved diagram supposed to show the variability in woman's capacities at the different times in her twenty-eight-day cycle.