ON SKISMOLOGICAL INVESTIGATION. 267 



rently accompanying fluctuations in barometric pressure at the time of a 

 storm in the distant Alps are all recorded. 



Two pendulums which hang side by side had lengths of 1 '50 meti'e, and 

 carried weights of 100 kilos. Side by side with one of these was a bar of 

 steel, about 1-5 metre in length and 10 cm. broad, firmly fixed at one end 

 and bent downwards at the other by a load of 45 kilos. The object of 

 this is to recoi'd vertical motion. 



The full period of this loaded spring is I'l sec. Its outer end is 

 connected by a system of levers with a writing point which rests on a 

 surface of smoked paper side by side with the writing indices of hori- 

 zontal motion connected with the ordinary pendulum. (For a short 

 description of the ordinary pendulum see British Association Report, 

 1896, p. 221. For a complete description see ' I Microsismograli dell' 

 Institute di Fisica della R. Universita di Padova : ' Dr. Giulio Pacher. 

 Atti del R. Instituto Veneto di Scienze, Lettre ed Arti, tomo viii. 

 .serie vii. 1896-971 



In another room there is a .similar pendulum, ■which is, however, 11 

 metres in length and carries a much heavier load (400 kilos.). In addition 

 to the two systems of levers for horizontal motion, projecting from the 

 bottom of the pendulum is a light pantograph, whicli gives a resultant 

 motion. The cliagram from this latter arrangement is one from which 

 the direction of various vibrations can be easily seen. 



The principal feature in the Vicentini and Pacher seismographic 

 arrangements are, first, tlie large masses that are used as steady points ; 

 and secondly, the ingenious and beautiful manner in which movements 

 relatively to these are mechanically magnified and recorded with a mini- 

 mum of friction. In all instances the magnification is 100-fold. Light 

 levers to magnify movement relatively to an approximately steady mass 

 have been used by Wagner, Gray, Bouquet de la Grye, Agamennone, 

 Brassart, and very many others. I myself have had perhaps 100 pieces 

 of apparatus thus provided, but in no instance when the multiplication 

 exceeded 20 have I been successful — so long as tlie method was mecha- 

 nical — to reach conditions so satisfactory as those attained by Vicentini. 

 Rather than multiplying the relative motion of the pendulum by a single 

 lever, Vicentini employs two short levers, each with a multiplication of 

 10. These are extremely light, balanced, and connected by an ingeniously 

 constructed link (see refei'ences mentioned above). The last lever carries a 

 writing index made from a glass fibre. A piece of glass rod is heated by 

 a blowpipe and flattened with pincers. The flattened portion is again 

 heated and drawn out as a long^^a^ fibre about 1 mm. broad. This when 

 broken into lengths each of 4 or 5 ins. is sufficient to form several 

 pointers. One of these is taken and one end of it heated and drawn out 

 to still smaller dimensions. The thin end oE this is rounded by bringing 

 it for an instant into contact with the edge of a small flame. To attach 

 such a fibre, say, to the end of the boom of a horizontal pendulum this 

 latter is tipped with a fragment of wax. This is heated with a taper and 

 the thick end of the fibre stuck on to the boom. 



We may now imagine the fibre to be floating freely as a ^prolongation 

 of the boom a centimetre or so above the smoked surface on which it is 

 to write. To bring it into contact with this surface a very small flame 

 is placed for a moment beneath the fibre within 3 or 4 cm. of its end, 

 when the rounded point falls upon the smoked surface and is then in 

 adjustment. 



