1877*] Q }1 Scientific Method. 495 
ential equations, which, if written out in full, might perhaps 
belt the earth. 
In physical science our ignorance is practically infinite as 
compared with our knowledge ; and when we come to mental 
and moral phenomena we are almost without any data on 
which to base strictly scientific reasoning. Each human 
being presents the phenomenon of a mass of conflicting 
hopes, fears, desires, passions, and inclinations which science 
can never hope to classify. How shall we measure these 
mental phenomena ? How shall we weigh accurately the 
emotions even of the least emotional of human beings ? 
What units shall we employ ? How shall we calculate the 
effects of each human life upon the general life of the com- 
munity ? We cannot hope ever to reduce these things 
within the grasp of rigid quantitative analysis. As Prof. 
Jevons has truly remarked : — “ As astronomers have not 
yet fully solved the problem of three gravitating bodies when 
shall we have a solution of the problem of three moral 
bodies?”* And shall “ victorious analysis” ever dream of 
attempting to bring under her formulae the faCts concerning 
man’s relation to the physical world around him ? If each 
set of phenomena, physical and mental, considered apart 
from the other, far surpasses our powers of investigation, 
how can science ever hope to approach the problem of the 
mutual relations of the two? “ The air itself is one vast 
library, on whose pages are for ever written all that man 
has ever said or even whispered. These, in their mutable 
but unerring characters, mixed with the earliest as well as 
the latest sighs of mortality, stand for ever recorded — vows 
unredeemed, promises unfulfilled, perpetuating in the united 
movements of each particle the testimony of man’s change- 
ful will.”t We cannot solve the mystery of the physical 
world, nor the mystery of the mental world, nor the mystery 
of the connection between the two. 
But we do attempt nevertheless to lessen the sphere of our 
ignorance and to change the unknown into the known. We 
endeavour to explain faCts by grouping them together under a 
generalisation. The wider generalisations of science are gene- 
rally called laws. Having made a bold generalisation, having 
appealed to faCts and found that our generalisation stands 
the test in any instance, we are very liable to conclude that 
this generalisation must hold good in all cases, and to give to 
the expression a coercive value. Indeed, the name law almost 
* Principles of Science, vol. ii., p. 458. 
f Charles Babbage, Ninth Bridgewater Treatise, p. 113. 
