FREQUENCY OF OBSERVED UNIFORMITIES. 147 



thrust themselves on the attention. Or the long-delayed 

 discovery of the microscopic forms of life, with all the phe 

 nomena they present, may be named as very clearly showing 

 how certain groups of relations not ordinarily perceptible, 

 though in other respects like long- familiar relations, have 

 to wait until changed conditions render them perceptible. 

 But, without further details, it needs only to consider the 

 inquiries which now occupy the electrician, the chemist, 

 the physiologist, to see that science has advanced, and is 

 advancing, from the more conspicuous phenomena to the less 

 conspicuous ones. 



How the degree of absolute frequency of a relation affects 

 the recognition of its uniformity, we see in contrasting certain 

 biological facts. The connexion between death and bodily 

 injury, constantly displayed not only in men but in all in- 

 ferior creatures, was known as an instance of natural causa 

 tion while yet deaths from diseases were thought super 

 natural. Among diseases themselves, it is observable that 

 unusual ones were regarded as of demoniacal origin during 

 ages when the more frequent were ascribed to ordinary 

 causes : a truth paralleled among our own peasantry, who by 

 the use of charms show a lingering superstition with respect 

 to rare disorders, which they do not show with respect to 

 common ones, such as colds. Passing to physical illustra 

 tions, we may note that within the historic period whirl 

 pools were accounted for by the agency of water-spirits ; but 

 we do not find that within the same period the disappearance 

 of water on exposure either to the sun or to artificial heat 

 was interpreted in an analogous way : though a more mar 

 vellous occurrence, and a much more complex one, its great 

 frequency led to the early recognition of it as a natural uni 

 formity. Hainbows and comets do not differ much in con- 

 spicuousncss, and a rainbow is intrinsically the more involved 

 phenomenon ; but chiefly because of their far greater com 

 monness, rainbows were perceived to have a direct dependence 



