transfer of matter from the centre, by way of the poles, to the equator, must be the establishment of counter-currents from the equator in diametrical lines, to the centre. Mark now the changes of temperature that must occur in these currents. An aeriform mass ascending from the centre towards either pole, will expand as it approaches the surface, in consequence of the diminution of pressure. But expansion, involving an absorption of heat, will entail a diminished temperature; and the temperature will be further lowered by the greater freedom of radiation into space. This rarefied and cooled mass must be still more rarefied and cooled in its progress over the surface of the spheroid to the equator. Continually thrust further from the pole by the ceaseless accumulation there, it must acquire an ever-increasing rotatory motion and an ever-increasing centrifugal force: whence must follow expansion and absorption of heat. To the refrigeration thus caused must be added that resulting from radiation, which, at each advance towards the equator, will be less hindered. And when the mass we have thus followed arrives at the equator, it will have reached its maximum rarity and maximum coolness. Conversely, every portion of a current proceeding in a diametrical direction from the equator to the centre, must progressively rise in temperature; in virtue alike of the increasing pressure, the gradual arrest of motion, and the diminished rate of radiation. Note, lastly, that this circulation will go on, but slowly. As the matter proceeding from the equator towards the centre must have its rotatory motion destroyed, while that proceeding from the poles to the equator must have rotatory motion given to it, it follows that an enormous amount of inertia has to be overcome; and this must make the currents so slow as to prevent them from producing anything like an equality of temperature. Such being the constitution of a concentrating spheroid of gaseous matter, where will the gaseous matter begin to condense into liquid? The usual assumption has been, that in a nebulous mass approaching towards the planetary form, the liquefaction will first occur at the centre. We believe this assumption is inconsistent with established physical principles. Observe first that it is contrary to analogy. That the matter of the Earth was liquid before any of it became solid, is generally admitted. Where has it first solidified? Not at the centre, but at the surface. Now the general principles which apply to the condensation of liquid matter into solid, apply also to the condensation of gaseous matter into liquid. Hence if the once liquid substance of the Earth first solidified at the surface, the implication is that its once aeriform substance first liquified at the surface.