C Lloyd Morgan — Physiography. 251 



time the apple has shrunk in size, the fruit having contracted within 

 the skin, which, no longer tight and glossy, is now wrinkled and 

 puckered up. 



But just as in the apple, so too in our planet, there is an inner 

 portion which is contracting, and an outer portion which does not 

 shrink : and as surely as the earth is losing heat by radiation into 

 space, her mass contracting and her size growing less, so surely must 

 the outer portion become puckered up, the most prominent wrinkles 

 forming what we call mountain ranges. 



While sun-heat, therefore, enables rain, rivers, and the sea to 

 denude the land and to combine in the formation of new continents, 

 earth-heat causes a fresh supply of land to be raised above the waters. 

 Were it not for this earth-heat England, as already mentioned, would 

 during the course of geological time be entirely washed into the 

 ocean of geological bankruptcy. All geological action, except that 

 due to the tides, is brought about by sun-heat or by earth-heat. 



Before inquiring what is the cause of this sun-heat and this earth- 

 heat, there is one more question to be answered. Of what does the 

 air, the water, the cliff, ultimately consist? Are earth, air, and 

 water, as the ancients believed, elements ? No. The air is composed 

 chiefly of a mixture of a gas called Nitrogen with one-fifth of its 

 volume of Oxygen. It is not difficult, as will be seen in Professor 

 Huxley's book, for the chemist in his laboratory to separate these two 

 gases. Nor has he much difficulty in splitting up water into the two 

 gases oxygen and hydrogen ; while the further task of ascertaining 

 of what the solid crust of the Earth is composed, though it requires 

 more labour, is by no means beyond his powers. But whereas water 

 contains but two elements, in the solid crust of the earth there are 

 about sixty-five. But what are these elements? They are simple 

 bodies which resist every effort of the chemist to decompose them 

 into simpler bodies. Many chemists, however, believe that, though 

 we cannot by any means at our disposal thus split them up, this is 

 only because the means at our disposal are limited, and that, at an 

 intensely high temperature, all would be found to consist of one 

 primitive form of elementary matter. 



One of the most striking results of modern scientific inquiry is 

 the discovery, by means of the spectroscope, that there exists in the 

 Sun's photosphere some sixteen or seventeen at least of the so-called 

 elements, with which we are acquainted on the surface of our earth. 

 Herein lies one of those many bonds, by which we are connected 

 with our central luminary. The cause of these bonds ; the origin of 

 sun-heat and earth-heat ; and of the Sun and the Earth themselves, 

 now require elucidation. 



According to the now-generally-accepted theory, known as the 

 Nebular Hypothesis of Kant and Laplace (and it must be noted that 

 we are here passing from the well known to the less known), our 

 solar system was formed from a diffuse nebulous mass. We must 

 imagine that this rotating spheroid mass once extended to the fui-thest 

 limits of the solar system ; beyond the orbit of Neptune. It radiated 

 heat freely into space, and under the force of gravitation underwent 



