3 i6 THE POPULAR SCIENCE MONTHLY. 



longer pendulum is suspended. The four pendulums are each con- 

 nected just above their bobs to the central pendulum with loose silk 

 threads. Fixed to the center of each of these threads, and held verti- 

 cally by a light spring, is a needle, so adjusted that each thread is de- 

 pressed to form an obtuse angle of about 155. These needles form 

 the terminals of an electric circuit, the other termination of which is 

 a small cup of mercury placed just below the lower end of the needle. 

 By a horizontal swing of one of the pendulums this arrangement causes 

 the needle to move vertically, but with a slightly multiplied amplitude. 

 By this motion the needle comes in contact with the mercury, and an 

 electro-magnet with a lever and pencil is caused to make a mark on a 

 band moved by clock-work. The five pendulums being of different 

 lengths, the apparatus is adapted to respond to seismic waves of differ- 

 ent velocities. 



Professor Rossi's microphone consists of a metallic swing arranged 

 like the beam of a balance. By means of a movable weight at one 

 end of the beam, this is so adjusted that it falls down until it comes 

 in contact with a metallic stop. The beam and the stop form two 

 poles of an electric circuit, in which is a telephone. The slightest 

 motion in a vertical direction causes a fluctuation in the current 

 passing between the stop and the beam, and announces itself in the 

 telephone. 



By observations made with instruments like these, it has been shown 

 that the soil of Italy is in incessant movement, with periods of exces- 

 sive activity, called seismic storms, that usually last about ten days. 

 The storms are separated by periods of relative calm. They are more 

 regular in winter, and exhibit sharp maximums in spring and autumn. 

 In the midst of such a period or at its end there is usually an earth- 

 quake. They have been observed to be generally related to baromet- 

 ric depressions. 



Earth-pulsations are slow but large undulations that appear to 

 travel over or disturb the surface of the globe. They are made mani- 

 fest through variations in the movement of pendulums, changes in the 

 position of the bubbles of levels, eccentricities in the behavior of 

 clocks, the swinging of chandeliers in churches, unusual disturbances 

 in bodies of water, and even of water in tubs, irregularities in the 

 flow of springs, and other phenomena, the occurrence of which, or 

 the peculiar manner of it, while it is consistent with the hypothesis 

 of such movement, can not be accounted for on any other probable 

 supposition. 



