On Lunar Periodicities in Earthquake Frequency. 457 



at all upon either steam or carbon dioxide. Magnetic oxide of iron 

 is the final product of the action of steam or of carbon dioxide at a 

 high temperature upon metallic iron : 



3Fe + 4H 2 = Fe 3 4 + 4H 2 . 

 3Fe + 4C0 2 = Fe 3 4 +4CO. 



Now, metallic iron has been detected in basalts and some other 

 rocks by Andrews (' Brit. Assoc. Rep./ 1852, Sections, p. 34), and 

 by other observers (e.g., G. W. Hawes, * Amer. J. Sci.,' Ser. 3, 

 vol. 13, p. 33), and I have verified this observation in the case of 

 the gabbro of Loch Coruisk. But it must be remembered that both 

 the reactions indicated in the equations just given are reversible, and 

 therefore the presence of metallic iron along with the magnetic oxide 

 in such rocks cannot be taken by itself as final proof that the oxide 

 and the associated gases, hydrogen and carbonic oxide, are the pro- 

 ducts of the action of steam and carbon dioxide upon metallic iron. 

 The presence of marsh gas in these rocks and the production of large 

 quantities of hydrocarbonous gases, as well as liquid petroleum, in 

 many parts of the earth's surface, tend to support the view, which is 

 apparently gaining ground, that in the interior of the earth's crust 

 there are large masses, not only of metal but of compounds of metals, 

 such as iron and manganese, with carbon. Assuming the existence of 

 such material, it is easy to conceive how, by the action of water at an 

 elevated temperature, it may give rise to metallic oxides and mixtures 

 of hydrogen with paraffinoid and other hydrocarbons. This view was 

 put forward some years ago by Mendelejeff (" Principles of Chemis- 

 try," Translation by Kamensky and Greenaway, vol. 1, 364 365), 

 and it has lately received further support from the results of the 

 study of metallic carbides, which we owe especially to Moissan (' Roy. 

 Soc. Proc.,' vol. 60, 1896, pp. 156160). 



" On Lunar Periodicities in Earthquake Frequency." By 

 C. G. KNOTT, D.Sc., Lecturer 011 Applied Mathematics, 

 Edinburgh University (formerly Professor of Physics, 

 Imperial University, Japan). Communicated by JOHN 

 MILNE, F.R.S. Received November 4, 1896, Read 

 February 4, 1897. 



(Abstract.) 



1. Introduction. The paper is a discussion of Professor Milne's 

 Catalogues of 8331 earthquakes, recorded as having occurred in 

 Japan, during the eight years 1885 to 1892 inclusive. These 

 catalogues, forming vol. 4 of the ' Seismological Journal of Japan, 7 



