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But no person whose mode of thought is logical can rest satisfied

with this condition of things. He asks: "How does it come that

certain reference-bodies (or their states of motion) are given

priority over other reference-bodies (or their states of motion)?

_What is the reason for this preference?_" In order to show

clearly what I mean by this question, I shall make use of a

comparison.

I am standing in front of a gas range. Standing alongside of each

other on the range are two pans so much alike that one may be

mistaken for the other. Both are half full of water. I notice

that steam is being emitted continuously from the one pan, but

not from the other. I am surprised at this, even if I have never

seen either a gas range or a pan before. But if I now notice a

luminous something of bluish colour under the first pan but not

under the other, I cease to be astonished, even if I have never

before seen a gas flame. For I can only say that this bluish

something will cause the emission of the steam, or at least

possibly it may do so. If, however, I notice the bluish something

in neither case, and if I observe that the one continuously emits

steam whilst the other does not, then I shall remain astonished

and dissatisfied until I have discovered some circumstance to

which I can attribute the different behaviour of the two pans.