EARTnUTJAKES OF NOV. in TO DEC, M, 1800. 619 



recorded bv observers -who paid such close attention to the earth- 

 quakes that their evidence is, I believe, sudicient to attest their 

 seismic origin. I have, however, thought it best not to depart from 

 the excellent rule laid down by the Swiss Seismological Commission, 

 and have inserted these under the heading of " Doubtful Shocks " 

 instead of in their proper chronological order. 



In the following accounts the time of occurrence is given in 

 Greenwich mean time, the hours being numbered from to 24, but 

 it is necessary to remark that for several reasons the times here re- 

 corded can at best be regarded as approximations only. The intensity 

 is estimated by means of the Rossi-Forel scale. In considering the 

 position of the seismic focus and of the epicentrum I refer, for this 

 purpose only, to its centre of intensity for the former, and to the 

 point vertically above it on the earth's surface for the latter. Fol- 

 lowing the notation of M. Porel, I have divided the shocks into 

 priiuipal and accessory. These are denoted by capital and small 

 letters respectively. 



II. Principal Shock, K: ^N'ov. 15, IT*' oO"". 



Intensity.— VII. 



Epicentrum.— Lat. 57° 25' 0" N., long. 4° 10' 50" W., i. e. ^ miles S. 

 21° E. of Inverness. 



Of this earthquake, the most intense of the series, I have 160 

 records from 115 different places. For the observations at eleven 

 of these I am obliged to trust to newspaper accounts alone. The 

 rest are given in the form of replies to my printed questions, and in 

 nearly every case are carefully made and possess a high value. 



1. Disturbed Area. — The map accompanying this paper refers 

 principally to this earthquake. On it are maiked, with very few 

 exceptions, all the places where the shock was felt. These are in- 

 dicated b}' small discs. Places where earthquake-sounds were 

 heard at the same time are denoted by crosses ( + ), drawn through 

 the discs when the shock was also felt, or separately if the shock 

 passed unperceived. The two continuous lines arc isoseismal lines 

 of intensities V. and IV. respectively ; the dotted lines represent 

 the boundaries of the disturbed areas of three of the subsequent 

 shocks. (See next page.) 



Outside the isoseismal of intensity lY. I have records from only 

 16 places, and these are not sufficient to determine exactly the 

 boundary of the disturbed area. Except towards the north, how- 

 ever, none of these places is more than ten miles from the isoseismal. 

 At Helmsdale there is an increase of intensity, and I am by no 

 means certain that this was not caused by a separate, but perhaps 

 not independent, earthquake. 



The area disturbed by the earthquake within the isoseismal of 

 intensity IV. is 86| miles long and 61 1 miles broad, the longer axis 

 being directed N. 52° E. and S. 52° W. The area contained by this 

 curve is about 4340 square miles, including the part covered by 

 the sea. 



