ON SEISMOLOGICAL INVESTIGATIONS. 43 



which do not reach distant stations. Although a list might be made of 

 earthquakes recorded at the European stations here considered, but not 

 at the thirteen widely separated stations indicated in the above table, 

 an inspection of this table shows the converse to be equally true, there 

 having been many earthquakes recorded in the south of South America, 

 on the east and west of North America, in South Spain, and in Great 

 Britain which have apparently escaped record in Central Europe. 



In connection with this subject attention may be drawn to the list of 

 earthquakes on pp. 44-46. As this list has been drawn up with great care, 

 it may be taken for granted that all entries which refer to approximately 

 the same times represent seismic disturbances. The larger of these will 

 have been recorded at distant stations. To determine whether this is 

 true for the smaller records observers are asked to make a close inspection 

 of their photographic traces. 



Experiments upon Piers. — At the end of March Professor H. H. Turner, 

 F.R.S., visited Shide, where, in conjunction with your Secretary, he 

 measured the stiflfness of various piers employed to carry seismographs. 

 To make a measure of this desci'iption a rope was tied round the column 

 to be tested about 2 inches from its top. A spi'ing balance was attached 

 to this, and a pull of from 5 to 30 lb. was exerted, with the result that the 

 column was deflected. These deflections were measured by an astro- 

 nomical level standing on the column, and in certain instances also by 

 the deflection of the boom of horizontal pendulums. The stifFest column 

 tested was a 12-inch earthenware drain pipe, 3 feet in length. The appa- 

 rent deflection was 0''-09 per one-pound pull. A brick column 6 feet in 

 height, and in ci'oss-section 3 feet by 1 foot 6 inches, had per lb. pull a 

 deflection angle in directions parallel to its sides of 0"*192 and 0''-05, the 

 latter referring to its greatest width. 



II. On Earthquake Records obtained at Stations on different Geological 

 Formations. — The records referred to in this note were obtained at Kew, 

 Shide, Bidston, and Edinburgh. The instruments used were Milne 

 horizontal pendulums with photographic recording apparatus. They were 

 similarly installed, and, so far as it has been practical, were kept with 

 similar adjustments. The geological formations at these four stations may 

 be briefly described as follows : — 



Kew. — Thick alluvial deposits of the Thames Valley, which in their 

 upper parts at least are saturated with water. 



Shide. —Here the pier carrying the instrument rests upon the dis- 

 integrated outcrop of bedr. of chalk which form the east and west backbone 

 of the Isle of Wight. These beds plunge at a steep angle, to rise again a8 

 a series of chalk downs to the north of the Solent beyond Portsmouth. 



Bidston. — The Observatory at Bidston is situated on New Red sand- 

 stone. 



Edinburgh.—'Rla.ckiovd. Hill, on which the Royal Observatory is 

 situated, is a great sheet of ' f elstone ' or porphyrite of Paljeozoic age. 



The records obtained from these stations are as follows : — 



