Yol. 63J] OCHIL EARTHQUAKES OF 1900 TO 1907. 371 



(37) 1907, April 7th, 11.11 p.m. 



A very slight shock, hardly p erce ptit>le, was felt by two 

 independent observers at Menstrie, the accompanying noise being 

 the more prominent feature. 



(38) 1907, April 7th, 11.19 p.m. 



A slight shock, consisting of two vibrations, was felt at Menstrie. 



(39) 1907, April 8th, 6.45 a.m. 

 A slight shock was felt at Menstrie. 



(40) 1907, April 11th, 5.30 a.m. 



A shock (intensity 4), accompanied by sound, was observed at 

 Uenstrie and Red Carr. 



(41) 1907, April 11th, 5.40 a.m. 



A shock (intensity 4) was felt at Airthrey, Menstrie, and Eed 

 €arr. 



(4.2) 1907, April 11th, 6.5 a.m. 



A shock, with very slight noise, was observed at Menstrie. 



III. Characteristics of the Ochil Earthquakes. 



The earthquakes described in the foregoing pages may be divided 

 into three classes, namely : (i) the principal earthquake of September 

 21st, 1905, which disturbed an area of about 1000 square miles; (ii) 

 the earthquakes of September 17th, 1900 (10.17 p.m.), July 23rd, 

 1905, and October 8th (7.24 a.m.), December 28th, and December 

 30th (4.15 p.m.), 1906, the average disturbed area of which was 

 100 square miles : and (iii) the remaining earthquakes, the disturbed 

 area of which rarely, if ever, exceeded 60 square miles. 



Time of Occurrence. — Of the 42 earthquakes described, 24 

 were felt during the night (6 p.m. to 6 a.m.), and 18 during the day 

 (6 a.m. to 6 p.m.). The slight preponderance during the night hours 

 is no doubt due to the conditions being then more favourable for 

 the observation of weak shocks. 



Nature of the Shocks. — When the shock was of intensity 

 equal to or greater than 4, it consisted almost invariably of one or 

 two prominent vibrations, generally followed by a brief tremor. 

 The shocks of intensity less than 4 were tremors only, though even 

 in these cases the accompanying sound frequently resembled the 

 report of a distant cannon or the noise caused by the fall of a 

 heavy weight. 



Sound-Phenomena. — The sound was heard by 84 per cent, 

 of the observers of the principal earthquake, by 90 per cent, of 



