CONDITION OF THE LAItGER PLANETS. 
39 
matters very little in what manufacture raw materials of a 
particular kind are employed, so that the manufacture affords a 
ready means of sorting them away and making room for fresh 
stores of them. The object of manufacture is to make articles 
which shall have real value, and raw materials are solely of use 
in so far as they can be employed in the manufacture of articles 
of such a nature. In like manner the object of theorizing or 
reasoning is to discover actual truths, and observations are only 
useful in so far as they enable us to discover such truths. The 
mere observer who argues that observation and not reasoning is 
real science, may be compared to an organ-blower who should 
argue that his work, not that of the organist, constituted real 
music. The organist cannot play without wind, the manu- 
facturer cannot get on without raw materials, and in like 
manner Kepler would never have established his laws without 
the observations collected by Tycho Brahe, nor would Newton 
have discovered the law of gravity without the raw material 
collected by Flamstead ; but as it is important in organ music 
that the wind be exhausted in melody not in mere noise, and 
important in manufacture that the raw material be employed to 
make useful not useless articles, so it is and has been a matter of 
considerable importance whether observations have been idly 
worked up in false systems like those of Ptolemy or Descartes, 
or wisely used to ascertain the truth, as by Copernicus, Kepler, 
or Newton. 
The theory which is now to be considered is this, that the 
planets Jupiter and Saturn are still in a state of intense heat, 
being at a much earlier stage of planetary development than 
our earth or those four companion orbs, Mercury, Venus, Mars, 
and the moon (in one sense more specially a companion than 
the others) which have been called the terrestrial planets. 
At the outset it may be well to consider the evidence for the 
only other theory which has been advanced on the subject — the 
theory commonly accepted with apparently as little question as 
though it had been the result of long and profound investiga- 
tion, had been tested in every possible way, had been weighed 
and not found wanting by all the ablest astronomers the world 
has known. This is the theory that Jupiter and Saturn are 
bodies in the same condition as our earth. 
It is not easy to find any reasoning whatever bearing upon 
this theory. It would seem almost that so soon as Copernicus 
had shown that the planets do not travel round the earth as a 
centre, but the earth with the planets travel around the sun, 
the conclusion was at once adopted that the earth and the 
planets are of necessity bodies of the same nature ; and that as 
no one was at the pains to question this doctrine, it became 
gradually regarded as one that had been established by demon- 
