MACKIE — PEIMAEY TRANSLATION OF THE EAETH, 
203 
the earth, removing the earth's orbit to the confines of celestial space 
could not increase that velocity by a mile, an inch in a second, if the 
resisting medium remained the same. The force that started gave 
the velocity, and the earth must get an additional kick, so to speak, 
while running, to have its orbital velocity increased. Now force acts 
equally in all directions ; and if a grain of gunpowder were exploded 
in mid air, it would blow out in all directions alike. So if any ex- 
plosion or explosive condensation of nebulous matter took place in 
space, it would act in all directions alike ; it would be a sphere of 
explosion, or a globular result from the condensation of matter within 
a given spherical area of space. The motion of such an explosion 
would be like sunliglit radiating in every direction; the motion pro- 
duced by such a condensation would be exactly the reverse, or like 
the crushing in-rush of air into an exhausted globe of glass — an in- 
coming to a central spot from all around. Neither explosion nor 
condensation in space could give rise to projectile-force; and if there- 
fore this world was formed by the condensation or the explosion of 
nebulous matter, neither that condensation nor that explosion could 
cause the translation of our resulting earth from one part of space to 
another. There could be no projection of a world in space luitliout a 
wall or fulcrum of denser space for the projecting force to act against. 
A cannon ball could not be projected from an open tube ; the gases 
of the gunpowder in the cannon act against the breach and find a 
fulcrum there. Where are gases exploding in open celestial space to 
find a wall of resistance that shall give the explosion a projectile- 
force ? We cannot conceive, Neitlier explosion nor condensation 
therefore could give rise either to direct or to revolutionary orbital 
motion round the sun ; it is impossible. It even seems more natural 
to seek for the causes of planetary orbital motion in motions of the 
ether of space. The incandescence of the sun must put any ethereal 
matter surrounding it for millions upon millions of miles around in a 
state of intense vibration. If the sun be in combustion — and spec- 
tral analysis shows it to be — oxygen or some other combustion-sup- 
porting gas must, one would fancy, be constantly indrawn towards 
it; while the heated and unburnt particles of the ether of space, or of 
the products of combustion, would as constantly be driven out into 
space. Might there be thus produced in the circumambient area 
around our luminary constant in-settings and out-settings of gaseous 
particles the friction of which against a free spherical planet might 
effect a rotatory motion of it ? If so, would the length of day and 
