Problems of life and mind, by George Henry Lewes. First series: The foundations of a creed ...

306 PROBLEMS OF LIFE AND MIND.
readily be conceived vibrating with different nodes, like a
rod or cord; and the principle of the superposition of
small oscillations may be applied to nerves as to rods.
103. Whether an hypothesis refers to the Agent or the
Agency, the one thing needful to be steadily borne in
mind is the one thing comm-only neglected, namely, that
while any supposition which can furnish aid is justified
by the assistance we derive from it, no supposition can be
accepted for more than instrumental aid, no supposition
can be allowed to take the place of a truth, until it has
itself been submitted to the operations which establish
a truth. An hypothesis may be false, yet help us to a
truth; but no demonstration of the truth of any process
proves that the hypothesis which explains the process is
true. The existence of Ether is not demonstrated because
the hypothesis of an Ether is the most satisfactory means
we have at present of explaining luminous phenomena;
all that is proved is that the hypothesis is effective. This
caution is the more needful because of our tendency to
consider the verification of a result as a proof of the independent truth of the hypothesis. Because the supposed
Agency is adequate, is it therefore to be held as existent?
Laplace mentions an example of the danger Nwhich besets
auxiliary hypotheses, " quand on les realise au lieu de les
regarder comine des mooyens de soumettre les observations
au calcul." Dominic Cassini, lie says, in forming a table
of refraction, started from the simple supposition of a constant density in the atmosphere. This table was exact at
the heights at which the stars are usually observed, and
was adopted by astronomers; and the hypothesis that the
refraction augments with the elevation gained universal
acceptance until Bouger proved, by observations made at
Quito, that the refraction at that heiglmt instead of being
inlcreaseci was dim-inished.*
* LAPLACE, Ezxposition du Syste7e dcl l~onde, 1. 191.