B. TERRESTRIAL PHYSICS AND METEOROLOGY. 121 



while the upper thermometers during that year were exposed 

 to an unusually mild temperature. Schriften Ostpreussische 

 physikalkch.-o'konoin. Gcsells.^Konigsberg^ XV., 18. 



THE INTERIOR STRUCTURE OF THE EARTH. 



The mode of formation of the inequalities of the earth's 

 surface forms the subject of a thorough study by Osmond 

 Fisher, in a memoir published in the twelfth volume of 

 the Cambridge Philosophical Transactions. He concludes 

 that the molten earth first solidified from the centre, and, 

 after a time, from the surface also ; so that there is probably 

 at present a thin layer of molten material between the so- 

 lidified crust and the solidified interior ; and that the solid 

 crust therefore rests in corrugations upon a liquid or quasi- 

 liquid layer. The conditions of equilibrium of such a crust 

 are, first, that it must be considered flexible ; second, it must 

 be in unstable equilibrium ; and, third, therefore oscillations 

 of the surface are possible. Mr. Fisher makes an approxi- 

 mation to a rigorous mathematical investigation by inquir- 

 ing what form would be assumed by a heavy, flexible crust 

 resting upon a liquid in a rectangular trough shorter than 

 the crust ; and shows that when any extraneous force acts 

 upon the crust, it will assume the form of a series of equal 

 circular arcs. The same conclusion holds good when the 

 trough is supposed to be very long, and opened lengthwise 

 into a circular form corresponding to the surface of the 

 earth. 



The further conclusions of Mr. Fisher are expressed in the 

 mathematical equations introduced by him. Cambridge 

 Philosophical Transactions^ XII. 



THE THERMAL SPRINGS OF THE UNITED STATES. 



A very complete list of thermal springs in the United 

 States, with the temperatures of their waters as far as they 

 have been observed, is given by Mr. G. K. Gilbert, of the 

 Survey of the Territories West of the Mississippi. He con- 

 siders the thermal springs as being a valuable indication of 

 the method by which inequalities of the earth's surface have 

 been formed. Hot springs are generally found where the 

 rocky structure is such as to admit of easy communication 

 with subterranean waters. Tilting and fracture of strata are 



F 



