298 Mr D. Milne on Earthquake-Shocks in Great Britain^ 



at any other season. " On an average of three years (says 

 the writer of the article Meteorology in Brewster's Encyclo- 

 paedia) we have found that, for the six months beginning with 

 April and ending with September, the mean monthly range 

 of the barometer is to that of the six months in the propor- 

 tion of five to eight." It will be remembered that the earth- 

 quake-shocks in this and in other European countries are, dur- 

 ing the same six months of summer, less than during the rest 

 of the year, in very nearly the same proportion. 



Mr Gilfillan of Comrie seems to have thought, that earth- 

 quake-shocks there were very frequent about the time of new 

 and full moon, as may be seen from the extracts given in the 

 register under dates May 1793 and 21st March 1795. This 

 opinion, if well founded, would afford an additional confirma- 

 tion, though a slender one, of the connection between earth- 

 quake-shocks and a diminished atmospheric pressure ; as it 

 has been ascertained that the barometer is slightly lower than 

 usual, at these periods of the moon's age.* 



In the earthquakes of foreign countries, it has been so fre- 

 quently noticed that the barometer fell at or about the time 

 of the shocks, that it is scarcely possible to doubt the connec- 

 tion between the two phenomena. Thus Humboldt, writing 

 at Cumana in South America, relates, that, " on the 18th 

 August 1799, I was struck at finding the absolute height of 

 the barometer a little less than usual. There was on that day 

 eleven strong shocks of an earthquake at Carupano, twenty- 

 two leagues east from Cumana.''t In describing the pheno- 

 mena accompanying the earthquake which happened in the 

 evening of 4th November 1799, the same intelligent observer 

 says, " The barometer was lower than usual, but the course 

 or progress of the horary variations or little atmospheric tides 

 was in no respect interrupted. The mercury was j)f^ci8ely at 

 its minimum height, at the moment of the third and last shock, 



* Mr Luke Howard, on comparing the barometrical averages of eighteen 

 years preceding 1832 with the moon's declination, " thinks there is evi- 

 dence of a great tidal wave or swell in the atmosphere, caused by the moon's 

 attraction, preceding her in her approach to, and following her slowly as she 

 recedes from, these latitudes." (Philosophical Magazine for July 1841, 

 p. 553.) 



t Humboldt, vol. ii. p, 31C. 



