xliv GENERAL SUMMARY OF SCIENTIFIC AND 



well at Sperenberg conclusively demonstrate that as we descend 

 into the earth the rate of increase of the temperature steadily dimin- 

 ishes, and that therefore, at a given depth, the temperature must be- 

 come stationary. It follows that the origin of the internal heat of 

 the earth is to be looked for, not in the presence of an internal molt- 

 en nucleus, but in the chemical or other action going on in the strata 

 themselves. This result is, however, ably controverted by Dunker 

 and Moesta. 



In the A?iiiual of the Imperial Geological Institution at Vienna m'c 

 find an essay on springs and their formation, by Dr. E. Tietze. 



The study of the internal heat of the earth is much facilitated 

 by lists of thermal springs, such as that compiled by Dr. Gilbert, of 

 Professor Hayden's Survey, and publislied officially by him. The 

 connection between the thermal springs and the disturbed or un- 

 disturbed condition of geological strata is clearly shown by the 

 chart which accompanies Mr. Gilbert's j^aper. 



The submarine explosion at Hell-gate, under the direction of Gen- 

 eral Abbott, was taken occasion of for measuring the velocity with 

 which the shock was communicated through the earth. Four deli- 

 cate seismometers were established at stations distant respectively 

 5, 9, 8, and 13 miles. The velocities of transmission for the cor- 

 responding stations were respectively 39, 45, 83, and 53 hundred feet 

 per second. The shock received at each station was of the nature 

 of a continued vibration, and not a short, sharp one. The observers 

 at the stations lay upon the ground and listened to the rumbling of 

 the earth, which occurred simultaneously with the sound. The dis- 

 cordant determinations of the velocity probably should be attributed 

 to the various natures of the strata of rock and earth through which 

 the sound was transmitted. 



