Miscellaneous Intelligence. 157 



include the following insular districts, which are among the most 

 well-marked seismic regions in the world, namely, the Grecian 

 Archipelago, Japan, the Malay Archipelago, New Zealand, and 

 the West Indies. The average amplitude of the annual period 

 in these eleven cases is 0*16, and that of the semi-annual period 

 0*24 ; i. e., the average amplitude of the annual period is just 

 half that for all the districts examined, while in the case of the 

 semi-annual period the average amplitudes are the same. 



Origin of the Annual Period. — In this, the concluding, sec- 

 tion of the paper, an attempt is made to show that the annual 

 change in barometric pressure may be the cause of the annual 

 change in seismic frequency. It would be difficult to prove that 

 such a connection exists, but reasons are given which seem to 

 render it in some degree probable. 



The most probable cause of the origin of the majority of non- 

 volcanic earthquakes is the impulsive friction, due to slipping, of 

 the two rock-surfaces of a fault. Now, whatever be the causes 

 of seismic periodicity, it seems probable that they are merely 

 auxiliary, and determine the epoch when an earthquake shall 

 take place, rather than there shall be an earthquake at all. Pro- 

 fessor G. H. Darwin has shown that the vertical displacement of 

 the earth's surface by parallel waves of barometric elevation and 

 depression is not inconsiderable, and that it diminishes at first 

 very slowly as the depth increases. Since the fault-slip which 

 produces even a moderately strong shock must be very small, 

 and since the work to be done in such a case is, not the compres- 

 sion of solid rock, but the slight depression of a fractured mass 

 whose support is nearly, but not quite, withdrawn, the annual 

 range of barometric pressure does not seem incompetent to pro- 

 duce the effects observed. 



Comparisons between the dates of the maximum epochs of the 

 seismic and barometric annual periods are made in 31 of the dis- 

 tricts treated in this paper. The seismic maximum approxi- 

 mately coincides with the barometric maximum in 10 districts, 

 and follows it by about one month in 9, and by about two 

 months in 4, districts ; the other cases generally admitting of 

 some explanation. 



In several insular seismic districts, and especially in Japan and 

 New Zealand, the amplitude of the annual period is very small ; 

 and, if many of the earthquakes of these districts originate 

 beneath the sea, this should be the case ; for, in the course of a 

 year, as the barometric pressure changes, the sea will have time 

 to take up its equilibrium position, and thus the total pressure on 

 the sea-bottom will be unaltered. 



IV. Miscellaneous Scientific Intelligence. 



1. On the laws of organic growth. JBioplastology and the 

 related branches of Biologic research; by Alpheus Hyatt. 

 (Proc. Boston Soc. Nat. Hist., vol. xxvi, pp. 59-125.) — Prof. Hyatt 



