December 27, 1894] 



NATURE 



209 



a known interval of five minutes. He then locked the cellar, 

 and when he returned at 8'45 he was obliged to make a correc- 

 tion,' because the litjht-point had left the paper. Unfor- 

 tunately, he forgot to note down its exact place, but from the 

 inspection of the curve it is evident that at 5 '6', after a short 

 interval of steadiness between 5'25 and S'6i, the pendulum 

 received a sudden shock, which caused it to oscillate, and at 

 the same time produced a deflection, by which the light-point 

 was probably brought off the lower edge of the paper, from 

 which it was distant 4S mm. at the time of the shock. There 

 can be no doubt that such was the cause of the disappearance 

 of the curve, for the base-line runs on perfectly undisturbed, 

 which is a sign that the instrument continued to be in good 

 working order, as usually. From S'45 to 965 the motion is 

 small; and from 9'65 till Il'l6 the curve is nearly perfectly 

 steady. 



\\. 1 1 '16 a new disturbance begins; the range of motion is 

 very small at first, but increases to 5 mm. at li'45, and to 

 10 mm. at ii-6o ; at i2'io the disturbance, which is much like 

 the first one, comes to an end, and is again followed by a steady 

 part of the curve. 



At I2'26 commences the last disturbance, which at 1247 

 increases to 6 mm. Between I2'73 and 13 '03 no traces of the 

 curve are visible, and during this interval a displacement of 

 loi mm. has occurred, which indicates a deflection of the 



At II 05 a new disturbance begins, which increases suddenly at 

 11-36, diminishes a little at 123, and increases again at 1247 

 From 127 to i3'22no traces of the curve are visible. At I3'9. 

 the motion decreases considerably, and after another small in- 

 crease at I4'87 reaches its end at I5'I7. 



The figure shows that the motion at Nicolaiew is much more 

 considerable than at Strassburg. Whilst at the latter place the 

 whole disturbance is divided into four distinct parts, which are 

 separated by moments of nearly perfect steadiness, at Nico- 

 laiew the first and second, as well as the third and fourth part, 

 each form a continuous disturbance. 



If we denote by V the relative strength of a shock in a direc- 

 tion normal to that of the pendulum, by a the range of motion, 

 measured on the curve, by U and T the distance between the 

 photogra|jhic drum and the pendulum mirror, and the period 

 of oscillation of the pendulum, then we have the following 

 relation between the observations in two different places : — 

 V, ^a, AT., 

 V„ a. ■ fl-jT, 

 In the present case 



dy - l-8m., (/o = 4'6m., Tj = 170s., To = lo'2s., 



thus Sj?— • A shock of the same strength therefore produces 



at Nicolaiew a disturbance ij; times as large as at Strassburg. 



Strassburg 



s«.waa!,-'"'""*ti'* 



yH«»«»''*'"^^' 



^«>^tWMIIW«< 



Or. M. T. 



4 5 



Nicolaiew 



10 



12 



13 



14 



15 



16 



17 



Fig. I. — Earthquake Disturbance observed at Strassburg and .it Nicolaiew on June 3, 1393, 



pendulum towards the north. The motion continues to be 

 visible until I4'45 ; the curve then resumes its nearly steady 

 appearance, which is once again interrupted by small motion 

 at 14-95. 



(i) Nico.'au-w. — The following details were communicated to 

 me by Prof. Kortazzi, who informed me that on this day he 

 went down into the cellar one half-hour later than usually, at 

 6-54, when he found that the light-point had passed from the 

 paper on to the brass rod, which serves to clamp the paper, and 

 was swinging considerably. From this reason the light-point 

 could leave no traces on the paper between 5 95 and 6 62. The 

 disturbance is very large and of long duration. It commences 

 at 4-32 and reaches its first maximum at 4-80, when the range 

 iSi-bomm. Strong motion continues until 8-4. From the copy 

 of the disturbance, which Prof. Kortazzi kindly sent me, and 

 which is represented in the above figure, it appears that at about 

 S'77. Of iim. licfoic the light-point was prevented to trace a 

 curve, by passing on to the brass rod, the curve was suddenly 

 interrupted, which shows that the pendulum was performing 

 large oscillations. Between 9-72 and 1 1 '05 the motion is small. 



' In the original photograph the second part of the curve is much dis- 

 placed, in the s:ime way .is the third part after the interruption. This was 

 altered in the figure to economise space. 



NO. 13 13, VOL 51] 



In comparing the two curves, it is evident that the different 

 intensity of motion at the two places is not due to the difference 

 in the values of the instrumental constants. The reason why 

 the motion of the pendulum is so much stronger at Nicolaiew is 

 this, that the soil consists down to a great depth of sand, which 

 is particularly favourable for the development of strong motion. 

 In this respect Nicolaiew resembles the two former stations, 

 Potsdam and Wilhclmshaven. Many facts tend to show that 

 the soil at Strassburg, though often disturbed by small earth- 

 quakes of distant origin, never oscillates as much as at the fore- 

 named places. It would not be right, therefore, from the mere 

 look of the curves, to draw the conclusion that the earthquake — 

 if such was the cause of the disturbance — must have originated 

 at a place considerably nearer to Nicolaiew than to Strassburg. 



Until now I have not been able to find a record of a pheno- 

 menon which might possibly be connected wiih this disturbance. 

 From its size and duration, one ought to think that it must have 

 been caused by a strong catastrophe, surpassing anything that 

 has been reported during the last year from all parts of the 

 world. But it is strange that the magnetic recording instru- 

 ments at Potsdam have shown no trace of motion, and that 

 nothing is reported from the delicate seismological instruments 

 which are at work in Italy. 



