Professor Helmholtz, assuming that at the commencement the density of
the nebulous matter was a vanishing quantity, as compared with the
present density of the sun and planets, calculates how much work has
been performed by the condensation; how much of this work still exists
in the form of mechanical force, as attraction of the planets towards
the sun, and as _vis viva_ of their motion; and finds by this how much
of the force has been converted into heat.
The result of this calculation is, that only about the 45th part
of the original mechanical force remains as such, and that the
remainder, converted into heat, would be sufficient to raise a
mass of water equal to the sun and planets taken together, not
less than 28,000,000 of degrees of the centigrade scale. For the
sake of comparison, Professor Helmholtz mentions that the highest
temperature which we can produce by the oxy-hydrogen blowpipe,
which is sufficient to vaporise even platina, and which but few
bodies can endure, is estimated at about 2000 degrees. Of the
action of a temperature of 28,000,000 of such degrees we can form
no notion. If the mass of our entire system were of pure coal, by
the combustion of the whole of it only the 350th part of the above
quantity would be generated.
The store of force at present possessed by our system is equivalent
to immense quantities of heat. If our earth were by a sudden shock
brought to rest in her orbit--which is not to be feared in the
existing arrangement of our system--by such a shock a quantity of
heat would be generated equal to that produced by the combustion of
fourteen such earths of solid coal. Making the most unfavourable
assumption as to its capacity for heat, that is, placing it equal
to that of water, the mass of the earth would thereby be heated
11,200°; it would therefore be quite fused, and for the most part
reduced to vapour. If, then, the earth, after having been thus
brought to rest, should fall into the sun, which of course would be
the case, the quantity of heat developed by the shock would be 400
times greater.