1 879 -I °f Physiol Law. 277 
world is very full of people who are ready to make assertions 
upon subjects which are evidently too difficult for them — in 
many cases too difficult for any one — to handle with any 
degree of certainty; and it doubtless often happens that 
some who have meditated studiously for years upon some 
such subject, arriving at no satisfactory conclusion, are re- 
garded as objedts of profound commiseration by others, who 
rush upon conclusions like the unthinking horse into the 
battle. It is as natural that people should thus differ as 
that some should have darker skins, taller frames, or more 
irritable tempers than others. To what extent these, and 
other differences which we shall point out, are blameworthy, 
we cannot attempt to discuss, but shall study the mental 
habits of men in precisely the same spirit in which we would 
study the habits of other animals. But I wish to show some 
tangible reasons for thinking that there are very few subjects 
upon which we can dogmatise, and that in any case it is 
unnecessary. I wish to advocate the cultivation of intel- 
lectual modesty, not merely because it seems to me to be 
one of the brightest ornaments of the human mind, but be- 
cause of its vital connection with another cardinal virtue — 
intellectual honesty. 
Perhaps this end will be best attained by considering the 
difficulties which are met in the investigation of any subject, 
when the sole aim is to find out the truth of the matter, and 
I have thought it proper to point out some of the difficulties 
to which we are subject in arriving at our conceptions of 
physical law. 
The study of physical science has endowed the human 
mind with an attribute which is usually ascribed to and is 
thought to be characteristic of the Divine Mind. I refer to 
the power of prophecy. The astronomer can predict the 
position of the planets for generations to come, basing his 
predictions on the assumption — an unproved assumption — 
that only those causes which he has considered will aCt in 
the future, or, in other words, that the present order of 
things will continue. His power of prediction does not, 
however, extend indefinitely into the future, for there are 
doubtless many minor disturbances or perturbations, too 
small to be detected by the instruments which he can com- 
mand, without many centuries of observation, the effects of 
which will become plainly apparent after the lapse of ages, 
— that is to say, his power of prophecy is limited by his 
ignorance of certain faCts, and possibly by his inability to 
solve the equations involved in a complete discussion of the 
subject. 
