ELECTRO-MAGNETIC SEISMOGRAPH.. 427 



be sufficient to uotice one of them. A certain quantity of mercury hav- 

 ing been poured into this tube, a wire of iron or phitinum is put in the 

 branch with the greater diameter, and another phitinum wire is i)hiced 

 at a very small distance from the surface of the mercury contained in 

 the branch with the smaller diameter. 



On the surface of the mercury contained in the branch with the small- 

 er diameter is placed a floating piece of iron suspended hj a lino silk 

 thread, which passes over an ivory pulley, with a counter- weight so reg- 

 ulated that if the floating piece is raised by the mercury it remains sei»a- 

 ratedfrom it, (at the point to which it had been raised ;) and as the axis 

 of the pulley has attached to it a long and light needle, it is evident 

 that this needle will deviate when the floating piece rises, and that re- 

 maining fixed, it will indicate upon the arc of the graduated circle the 

 number of degrees it has traced. If there be a horizontal shock in the 

 direction of one of these tubes of mercury, the mercury will be agita- 

 ted m the two vertical branches, but, undergoing more perceptible oscil- 

 lations in the branch with the smaller diameter, it will raise the floating 

 piece of iron, and will cause the needle to deviate in a corresponding 

 manner. Bat at the same instant the mercury will touch the point of 

 the platinum wire, and the electric current, which will thus have pas- 

 sage, will excite the two electro-magnets before mentioned, and will act 

 in the same manner as already explained for vertical shocks. The 

 deviation of the needle will indicate the direction of the shock ; and if 

 the shock is not in the exact direction of the tubes, its real direction 

 will be indicated by two needles. 



By the aid of the electric current, shocks may be registered which 

 would otherwise escape notice on account of their extreme slightuess, 

 for the trembling of the surface has no resistance to overcome, pro- 

 vided that the points of platinum are placed very near the surface of 

 the mercury. I have added some auxiliary apparatus for shocks a little 

 more violent. For instance, I have placed at the base of the column the 

 mercury-apparatus of Coulier or of Cacciatore. At the extremity of the 

 metallic wire I have suspended a metal globe, which, in oscillating, 

 moves the light horizontal tubes by which it is surrounded. 



One clock is intended to make known with the precision of a half-sec- 

 ond the beginning of the shock ; but to know the hour in which the 

 shock occurs, the other clock will suflice ; for the length of the paper 

 unrolled by the wheel, and the hours marked by the needle, will indicate 

 sufficiently the time. This apparatus registers all the shocks that take 

 place, indicating the duration of each and the time that elapses between 

 them ; but it cannot give the nature and intensity of each of them. 

 By it we can know if all the shocks were vertical, and also their maxi- 

 mum intensity. We can likewise know if all were horizontal, and if 

 they had the same direction, or if the direction was different. We can 

 also know if there was one shock of one kind, and another of a dittereut 

 kind. This seemed to me sufficient for registering the movements (trem- 



