solid body. It seems very unlikely that there can be throughout its entire extent any portion which possesses the properties of a solid; certainly those exterior parts of the sun which are all that are accessible to our observation are anything but solid: they are vast volumes of luminous material floating in gases of a much less luminous nature. The openings between the clouds form the spots, while the mighty projections which leap from the sun's surface testify in the most emphatic manner to the gaseous or vaporous character of the outer parts of the great luminary. A gaseous globe like the sun when it parts with its heat observes laws of a very different type from those which a cooling solid follows. As the heat disappears by radiation the body contracts; the gaseous object, however, decreases in general much more than a solid body would do for the same loss of heat. This is connected with a striking difference between the manner in which the two bodies change in temperature. The solid, as it loses heat, also loses temperature; the gas, on the other hand, does not necessarily lose temperature even though it is losing heat. Indeed, it may happen that the very fact that the gaseous globe is losing heat may be the cause of its actually gaining in temperature and becoming hotter. This seems a paradox at the first glance, but it will be found not to be so when due attention is paid to the different notions that belong to the words h?at and temperature. The globe of gas unquestionably radiates heat and loses it, and the globe, in consequence of that loss, shrinks to a smaller size. The heat, or what is equivalent to heat, that is left in the globe, is exhibited in a body of reduced dimensions, and in that smaller body the heat shows to such advantage that the
