52 
by the fact that it accounted for the dissimilar fact of the pre- 
cession of the equinoxes. This indirect evidence is of more 
value than the direct, because in the case of the direct there is 
often a danger of our observations being somewhat warped by 
the prejudice of a wished-for result, but the indirect must be 
altogether honest. 
It sometimes happens that the result of experiment may 
approximate very closely, but not exactly, to that required by 
the hypothesis ; the divergence having been caused by some 
residual fact, which, when examined, strikingly confirms the 
hypothesis instead of weakening it. The law of the develop- 
ment of heat in elastic fluids by compression affords an illus- 
tration in its relation to the propagation of sound through the 
air. Newton calculated that sound ought to travel at the rate 
of 968 feet per second ; experiment however, at that time, 
showed it to travel at the rate of 1,142 feet. Here, then, was 
a residual velocity which Newton and others made many in- 
effectual attempts to explain. Laplace, however, suggested that 
it might arise from the heat produced by the condensation 
taking place at every vibration, increasing the elasticity of the 
air. In 1816 he published the theorem on which the connection 
depends. On applying it, the calculated velocity of sound 
agreed very closely with the best antecedent experiments, and 
thus this residual velocity strengthened the foregoing law of the 
development of heat by compression. There are many other 
characteristics of true evidence, and tests of the hypotheses 
inferred from it; there is much more that might be said regarding 
the evolving of science by the threefold process of observation, 
hypothesis, and verification ; but time will not permit. Indeed, 
the subject is so extensive, that I could only detach a small 
portion of the fringe ; and as this hasty paper has not been 
written for those who understand the subject far better thau I 
do, but for those who may not have given much attention to 
this special aspect of science, I hope I shall be pardoned for 
the superficial manner in which I have treated it. Before 
proceeding to apply these principles to cases of present theories, 
I must give you the character of the true naturalist as drawn 
by Professor Jevons and by Faraday. Jevons says, “ It would 
seem as if the mind of the great discoverer must combine 
almost contradictory attributes. He must be fertile in theories 
and hypotheses, and yet full of facts and precise results of 
experience. He must entertain the feeblest analogies, and the 
merest guesses at truth, and yet he must hold them as worth- 
less till they are verified in experiment. When there arc any 
grounds of probability, he must hold tenaciously to an old 
