30 



NATURAL SCIENCE. Jan.. 



unfortunately, it is not quite certain that they referred to the same 

 spots. 



Other evidence pointing to a sudden movement of the ocean-bed 

 is furnished by the seismic sea-waves. Wherever it was observed, 

 the sea first retired several metres — at San Stefano as much as 200 

 metres — and then, after some oscillations, returned to its original 

 level. On the opposite side of the Sea of Marmora and outside the 

 first isoseismal, however, no observations were made, and it is there- 

 fore uncertain whether the iirst retreat of the sea was universal. 



Earthquake-Pulsations. — The island of Crete appears to be the 

 most outlying district where the earthquake was actually felt, and this 

 is about 450 miles from Constantinople. But to a distance far beyond 

 this the pulsations spread outwards, and, as they passed each spot, 

 the ground there rocked slowly and gently to and fro through an 

 angle of, perhaps, not more than a fraction of a second. At Nicolaiew, 

 in the south of Russia, a horizontal pendulum was so strongly disturbed 

 that it was thrown out of position. At numerous stations in Italy, 

 long and heavy pendulums recorded the passage of the pulsations. 

 They were registered by magnetographs at Pola, Potsdam, Wilhelms- 

 haven, St. Petersburg, Utrecht, Paris, and even at Kew, which is 

 more than 1,560 miles from the seat of disturbance. 



In Fig. 2 is reproduced the record of the pulsations at Siena, 

 obtained with the aid of the Vicentini microseismograph. This 

 instrument consists of a heavy pendulum, from the base of which a 

 lever projects vertically downwards. The lower end of the lever is 

 connected with the short arms of two very light horizontal levers at 

 right angles to one another, and the longer arms of the latter end in 

 fine points which leave their traces on a strip of smoked paper driven 

 just underneath them by clockwork. Each of the divisions on the 

 intermediate straight line corresponds to an interval of one minute. 

 The record begins on the left side of the diagram, and for several 

 minutes the movement was so great that Professor Vicentini, who 

 happened to be watching the instrument, found it necessary to 

 displace the paper sideways to prevent one of the pens from 

 leaving the smoked surface. It will be seen from the figure that the 

 movement of the ground lasted for more than three-quarters of an 

 hour; and this was not due to the free swinging of the pendulum, for 

 the period of the pulsations near the close was several times greater 

 than the period of oscillation of the pendulum (9). 



At many places it is possible to ascertain the moments when the 

 first small movement became perceptible, and also when the larger 

 pulsations began and ended. If the time at which the earthquake 

 was felt at Constantinople were known with equal precision, we 

 should be able to obtain a good estimate of the velocity of the 

 pulsations. Unfortunately, this important element of the calculation 

 is not free from doubt. Mr. Coumbary gives the time at the Meteoro- 

 logical Observatory as 0-24 p.m. (Constantinople mean time). At 



