268 REPORT— 1898. 



For rapid motion the pendulums behave as steady points, and the 

 movements of the ground are multiplied 100 times, whilst for slow move- 

 ments the angular deflections of the pendulum are similarly enlarged. 



The records are received upon a continuous band of smoked paper 

 moving at a rate of 2 cm. per minute. This band hangs vertically, 

 passing over a roller above and round one below. The axes of these two 

 rollers are not parallel, with the result that the paper travels laterally 

 along the upper drum, and the traces drawn by the pens are parallel 

 spiral lines. Every minute, by electrical connections with a clock, time 

 marks are made upon the band. The Vicentini seismographs are now 

 installed at Rocca di Papa, Verona, Siena, and Laibach. 



Sfrasgbuiy. 



When I entered the mamificent buildin£;s which constitute the 

 University of Strassburg I felt that I was upon ground which the 

 investigations of the late E. von Rebeur - Paschwitz had made 

 classical. In a few minutes, in company with the genial Pi'ofessor 

 Gerland and his assistant Dr. E,. Ehlert, I was engaged in inspecting 

 seismograms from the Ehlert three-component pendulums. These are 

 recorded on a band of photographic paper, about 21 cm. broad, moving 

 at a rate of 12 cm. per hour. This, with chemicals and other materials, 

 costs about 36/. per year. By examining the traces with a magnifying 

 glass, it seems that they consist of a fine series of zigzags, indicating that 

 the pendulums are always in motion. Inasmuch as the removal of the 

 calcium chloride from the pendulum cases does not aCfect their move- 

 ments, and because the temperature changes in the chamber where the 

 pendulums ai-e installed is small, it is just possible that these movements 

 may be the result of the city traffic. If this is so, then the movements 

 should be less pronounced at night and more pronounced on public 

 holidays, and at times when traffic is unusually increased. The fact that 

 the tremors produced in a seismograph by a passing carriage or train 

 commence and end suddenly, however, weakens such a supposition. 



At present the pendulums are installed on an insulated column in a 

 chamber beneath the Astronomical Oljservatory (for description of the 

 apparatus see ' Beitrage zur Geophysik,' Band III. Heft 1-3). In the 

 original design of Von Bebeur a complete pendulum weighed 42 gms., 

 and two might be used at right angles to each other. 



Each of Dr. Ehlert's pendulums weighs 200 gms., and three are 

 arranged, at angles of 120° with each other, inside a cylindrical iron case. 

 The weights of these pendulums are at their outer ends, near the centre of 

 the casing. By screws from the outside of this case the vertical axes of 

 each of three pendulums can be inclined forwards or laterally. The adjust- 

 ments, therefore, are not dependent upon screws in a bed plate. The 

 greater weight concentrated at the outer end of each pendulum results in 

 greater certainty of obtaining a steady point for rapid movements of the 

 ground, and hence, perhaps, the continual movement. With three com- 

 ponents a direction of motion can be obtained, whilst a very slight move- 

 ment (the components of which might not be visible on two pendulums) 

 might be recorded on a pendulum to which its direction was nearly at 

 right angles. Each pendulum carries a mirror wliich reflects a beam of 

 light from a lamp standing near the record-receiving surface 4 metres 

 distant. In front of this there is a cylindrical lens to bring the beams to 

 a focus before impinging on the paper. The clock which drives this band 



