Manchester Memoirs, Vol. Iv. (1910), No. |. 3 



cooling as those outlined in the instance of the central 

 body. 



The notion that the earth and, inferentially, the other 

 planets are solid bodies throughout, finds no support from 

 a reasonable consideration of the constituents of the 

 earth's crust, so far as they are accessible to observation. 

 The late distinguished Professor of Geology in Oxford 

 University (Sir Joseph Prestwich), in his classical work 

 on Chemical, Physical, and Stratigraphical Geology, has 

 clearly demonstrated from the uplift of continental areas 

 and mountain chains, the welling out of basaltic lavas 

 over many thousand square miles of surface and of great 

 thickness, that a comparatively thin crust enveloping a 

 fluid interior is a necessary condition to satisfy the 

 requirements of geologists and physicists. More signifi- 

 cant still is the succession of foldings of the earth's crust 

 and stratigraphic contortions of small curvature, both of 

 which features indicate a thickness of solid crust less than 

 twenty-five miles. How far the imprisoned gases at the 

 centre of the earth and the aqueous vapours near the 

 surface may have contributed respectively to produce 

 these geological changes, it is unnecessary now to discuss, 

 but in the instance of the moon, which has neither water 

 nor an atmosphere, the evidence of intense volcanic action 

 manifested on its surface can only be accounted for by 

 the ejective force of the gaseous substances in its interior, 

 similar to that by which the incandescent gases from the 

 surface of the sun are projected. 



The fine series of photographic enlargements of the 

 moon executed by MM. Loev/y and Puiseux, of the Paris 

 Observatory, show the greater part of its surface, from 

 the equator to the poles, covered with extinct volcanoes 

 in every stage of formation, similar to those on the 

 terrestrial elobe. Some of these volcanoes are twelve 



