SECT. 11.] On certain kinds of Groups or Series. 15 



length. Or, again, it is perfectly possible that future gene 

 rations might prefer a short and a merry life, and therefore 

 reduce their average longevity. The duration of life cannot 

 but depend to some extent upon the general tastes, habits 

 and employments of the people, that is upon the ideal which 

 they consciously or unconsciously set before them, and he would 

 be a rash man who should undertake to predict what this ideal 

 will be some centuries hence. All that it is here necessary 

 however to indicate is, that this particular uniformity (as we 

 have hitherto called it, in order to mark its relative cha 

 racter) has varied, and, under the influence of future eddies 

 in opinion and practice, may vary still; and this to any 

 extent, and with any degree of irregularity. To borrow a 

 term from Astronomy, we find our uniformity subject to what 

 might be called an irregular secular variation. 



11. The above is a fair typical instance. If we had 

 taken a less simple feature than the length of life, or one 

 less closely connected with what may be called by compari 

 son the great permanent uniformities of nature, we should 

 have found the peculiarity under notice exhibited in a far 

 more striking degree. The deaths from small-pox, for ex 

 ample, or the instances of duelling or accusations of witch 

 craft, if examined during a few successive decades, might 

 have shown a very tolerable degree of uniformity. But these 

 uniformities have risen possibly from zero ; after various and 

 very great fluctuations seem tending towards zero again, at 

 least in this century ; and may, for anything we know, un 

 dergo still more rapid fluctuations in future. Now these 

 examples must be regarded as being only extreme ones, and 

 not such very extreme ones, of what is the almost universal 

 rule in nature. I shall endeavour to show that even the few 

 apparent exceptions, such as the proportions between male 

 and female births, &c., may not be, and probably in reality 



