398 Lord Kelvin on the Formation of 
which at present exist, the present condition of the universe 
might be very much the same as it is. Towards a speculative 
answer we might be guided, and perhaps wrongly guided, by 
what we see of meteorites, stony or iron. We can hardly 
regard it as probable that those broken looking lumps of solid 
matter, with their corners and edges rounded off by melting 
in their final rush through our atmosphere before arriving at 
the Earth's surface, were primitive forms in which matter 
either was created, or existed through all infinity of past time. 
On the contrary, it may seem to us quite probable that the 
primitive condition of matter was atomic ; perhaps every 
primitive particle was a separate indivisible atom ; or perhaps 
some of the primitive particles were atoms, and some of them 
doublets such as the 2 , N 2 , H 2 , which we know as the molecular 
constituents of gaseous oxygen, gaseous nitrogen, gaseous 
hydrogen, according to modern chemical doctrine. Or perhaps 
some of the primitive particles may have been given in groups 
consisting of a moderate number of atoms ready for building 
into crystals ; or they may have been given as very small com- 
plete crystals each consisting of a very large number of atoms. 
§ 2. To illustrate the dynamics of the real conglomeration, 
which we believe to be an event of ancient history, consider 
an ideal case of 1083 million million million cubic metres of 
solid matter ; the sum of their volumes being equal to the 
Earth's volume. Let the density of the material of each cube 
be equal to the Earth's mean density, 5*67. The sum of their 
masses will be 6*11 thousand million million million metric 
tons, being equal to the Earth's mass. Place them at rest in 
cubic order, equally distributed through a vast spherical space, 
of radius one thousand times the Earth's radius, and therefore 
of volume equal to a thousand million times the Earth's 
volume. Let every one of the cubes be oriented with its 
faces and edges parallel to the planes and lines of the cubic 
order. In this order, the lines of shortest distance between 
the centres of constituents are perpendicular to the three 
pairs of parallel faces of the cubes. The distance from centre 
to centre would be one metre, if the cubes were given in 
contact, occupying a sphere equal in bulk to the Earth. The 
distance between the centres of nearest neighbours is therefore 
a kilometre, when they are given in their wide spread initial 
arrangement. 
§ 3. Leave now the cubes all free to fall inwards in virtue 
of mutual gravitation. Each one of those on the bounding 
surface of the whole group wall commence falling towards 
the centre of the sphere, with acceleration one millionth of 
the acceleration of a body falling freely near the Earth's 
surface : that is to say 9*8 millionths of a metre per second 
