AIMS, ETC., OF SCIENTIFIC THOUGHT. 175 



had been wrongly stated. Cases were found of wonderfully compli- 

 cated structures that served no purpose at all; like the teeth of that 

 whale of which you heard in Section D the other day, or of the Du- 

 gong, which has a horny palate covering them all up and used instead 

 of them ; like the eyes of the unborn mole, that are never used, 

 though perfect as those of a mouse until the skull-opening closes up, 

 cutting them off from the brain, when they dry up and become inca- 

 pable of use ; like the outsides of your own ears, which are absolutely 

 of no use to you. And when human contrivances were more advanced 

 it became clear that the natural adaptations were subject to criticism. 

 The eye, regarded as an optical instrument of human manufacture, 

 was thus described by Helmholtz the physiologist who learned phys- 

 ics for the sake of his physiology, and mathematics for the sake of hi" 

 physics, and is now in the first rank of all three. He said, " If an op- 

 tician sent me that as an instrument, I should send it back to him with 

 grave reproaches for the carelessness of his work, and demand the re- 

 turn of my money." 



The extensions of the doctrine into physics were found to be still 

 more at fault. That remarkable property of pure water, which was 

 to have kept the sea from freezing, does not belong to salt-water, of 

 which the sea itself is composed. It was found, in fact, that the idea 

 of a reasonable adaptation of means to ends, useful as it had been in 

 its proper sphere, could yet not be called universal, or applied to the 

 order of Nature as a whole. 



Secondly, this idea has given way because it has been superseded 

 by a higher and more general idea of what is reasonable, which has 

 the advantage of being applicable to a large portion of physical phe- 

 nomena besides. Both the adaptation and the non-adaptation which 

 occur in organic structures have been explained. The scientific thought 

 of Dr. Darwin, of Mr. Herbert Spencer, and of Mr. Wallace, has de- 

 scribed that hitherto unknown process of adaptation as consisting of 

 perfectly well-known and familiar processes. There are two kinds of 

 these: the direct processes, in which the physical changes required to 

 produce a structure are worked out by the very actions for which that 

 structure becomes adapted as the backbone or notocord has been 

 modified from generation to generation, by the bendings which it 

 has undergone ; and the indirect processes, included under the head 

 of Natural Selection the reproduction of children slightly different 

 from their parents, and the survival of those which are best fitted to 

 hold their own in the struggle for existence. Naturalists might give 

 you some idea of the rate at which we are getting explanations of the 

 evolution of all parts of animals and plants the growth of the skele- 

 ton, the nervous system and its mind, of leaf and flower. But what, 

 then, do w r e mean by explanation f 



We were considering just now an explanation of a law of gases 

 the law according to which pressure increases in the same proportion 



