580 The Deceased Wife's Sister's Question : [October, 
experimental determinations, Fizeau’s and Foucault’s exceed 
only by 50,000 metres the proportion 20 to ig. My figure 
holding not quite the middle is, as it should be, somewhat 
nearer the minimum figure. Two or all three figures may 
not be quite correct, but it can be shown that the differences 
stand in a regular relation to the yi ^ 1655, yi 1713*9, 
yi 17 73, &c. — that is, to the inverse squares of the 
quantities expressing the various leading relations of solar 
to terrestrian gravity at the surface of the earth and through 
the atmosphere. 
II. THE DECEASED WIFE’S SISTER’S QUESTION: 
RATIONAL MARRIAGE-LAW. 
wT may at first glance appear strange that we should here 
discuss a subject commonly regarded as falling mainly 
^ within the province of divines and jurists. We sub- 
mit, however, that the entire question belongs solely and 
simply to the physiologist, and that as such it may with 
perfect right be considered in the “ Journal of Science.” 
The first rudiments of a Marriage-Law — that is, the first 
restrictions on union between any two individuals of opposite 
sexes — have to be sought in the vegetable world. All those 
most interesting arrangements described by Darwin and 
others, tending to prevent self-fertilisation and ensure cross- 
fertilisation, are an unwritten but effective law for keeping 
apart those who are too near of kin. This law is self- 
executive : seeds which have been fecundated by the male 
element of a strange plant, or at least by that of another 
flower of the same plant, — which is substantially another 
individual, — germinate more freely, and give rise to more 
vigorous plants, than such as have been from any cause 
fecundated by the pollen of the flower which produced 
them. 
If we pass to a consideration of the animal world we 
cannot fail to note a number of arrangements which tend to 
frustrate, or at least to render unlikely, sexual intercourse 
between kindred. Even among hermaphrodites, such as 
the slugs, self-impregnation is impossible, and the mutual 
