The Causes and Phenomena of Earthquakes. 53 



founded, till certain principles have been referred to ; and these 

 must necessarily be maintained on the basis of the arguments by 

 which they have been established. "We shall be safer in this way 

 than in any other ; and to some of the members of this Society, 

 it may be satisfactory to have the subject so initiated When we 

 consider that the literature of earthquakes extends already to 

 upwards of 2000 separate publications in various languages, it 

 may be better to avail ourselves of the labours of those who have 

 narrowed the field of research than to explore it anew in all its 

 ramifications. Mr. Mallet, to whose paper I have made allusion, 

 has given a catalogue of 500 or 600 works, enumerated by Pro- 

 fessor Perrey, of Dijon (who has himself contributed nearly 60 

 distinct treatises) in the Memoirs of the Imperial Academy of 

 Dijon (1845-6). 



Undoubtedly, there is sufficient known to establish a relation- 

 ship between the phenomena of earthquakes and volcanos. Facts 

 justify the assumption that whether preceding, accompanying, 

 or succeeding each other, eruptions and earthquake shocks are 

 often mutually dependent on each other; and thatcthey are so 

 dependent as to imply that they must have a common source, in a 

 fluid zone of matter with which steam and other gases are associated, 

 at a greater or less depth below the earth's surface. 



We have in this allusion been again brought face to face with 

 the question partly discussed at our July meeting, viz., the evidence 

 afforded to a theory of internal heat, by the fact arrived at in 

 artificial or natural openings at great depths in the crust of the 

 earth. Between the limits of 70 and 90 feet, with some excep- 

 tions, experiments have shown that the temperature in that ratio 

 increases from the surface towards the centre in degrees of 

 Fahrenheit's thermometer, allowing, of course, for the structure 

 and conditions of the strata traversed. The latest reliable ex- 

 periments are those detailed in the Anniversary address to the 

 Geological Society of London, delivered by Mr. Warrington 

 Smith, on 21st of last February. In Mr. Smith's remarks, 

 I find a full confirmation of the opinions respecting earth 

 temperatures which I ventured to express in our conversa- 

 tion in this room two months ago. And I am sure my learned 

 colleague, the Astronomer, would be much interested in the 

 details submitted by the accomplished geologist — Mr. Warrington 

 Smith — of the curious facts observed in relation to experiments 

 recently undertaken in France. From experiments by M. 

 Walferdin these results were obtained. In two places in the coal 

 field, near Creuzot (Soane and Loire), the experiments being 

 conducted exceptionally, and for the purposes of scientific truth, 

 it was shown that the earth's temperature varies at small distances. 

 At Mouillelonge, the depth equivalent to 1° F., was 43.1 feet, and 

 at Torcey, only two miles distant, it was 56 feet. Thus the tern- 



