2g6 



KNOWLEDGE & SCIENTIFIC NEWS. 



[December, 1905. 



a drawing-pin or nail vertically over the pin at-E. A 

 ver)' sligfht movement of the clock-case displaces the 

 wire E C, and the lath C D falls as before and stops 

 the clock. 



Marvin's Seismoscope. 



Professor Milne's si-ismoscope mav easily be con- 

 structed with home-made appliances. Tlie next two 

 instruments, designed by Professor C. F. Marvin and 

 Dr. G. Agamennone, are of less simple form. Pro- 

 fessor Marvin's seismoscope, which is in use in the 

 United States, is illustrated in fig. 3. A heavy weight 

 A is suspended from the frame B by means of a steel 



File. 3.— Marvin's Seismoscope. 



link C, which passes partly through the centre of the 

 weight. .At the bottom of the link is a small hole D, 

 into which fits the sharp point of a screw E rigidly 

 connected with the weight, and .so adjusted that the 

 point is just above the centre of gravity of the weight. 

 .At the top of the link is a similar pointed .screw F, 

 resting in a hole made in a projection G from the 

 frame B. When suspended in this manner, the weight 

 ;\ is obviously in stable equilibrium. From the top of 

 the link C there projects upwards a slender and flexible 

 pin H, about six inches long. 'Hie upp<-r end of the 

 pin is tipped with platinum and passes through a small 

 hole (also lined with platinum) in the plate K at the 

 top of the instrument. This plate is electrically insu- 

 lated from the frame B, but is connected bv a wire with 

 one of the binding screws L fixed to the base. Tlie 



position of the plate can be adjusted by means of four 

 screws M (onlv two of which are shown in the figure) 

 so that, when the seismoscope is in working order, the 

 tip of the pin H is exactly in the centre of the hole in 

 the plate. The binding screws L are connected with 

 the poles of a battery. 



When an earthquake occurs, the frame B moves with 

 the ground, but the heavy weight .A remains nearly at 

 rest. The movement of the frame with respect to the 

 weight is magnified several times at the upper end of 

 the needle H ; and. if the original displacement is great 

 enough, the tip of the needle touches the side of the 

 hole in the plate K, and completes the circuit. By such 

 means, a clock may lie stopped, and, if desired, an 

 electric bell may be rung to give notice that the clock 

 requires attention ; or a record may be made on a strip 

 of paper moved bv clockwork. 



The latter method is that which is employed in the 

 United States Weather Bureau, at Washington. 'Ilie 

 time-recorder there is the so-called " weekly anemo- 

 meter register." Tfiis consists of a horizontal cylinder 

 covered bv a sheet of paper and revolving by clockwork 

 once in six hours. .A pen rests lightly on the paper as 

 the latter passes underneath. The pen is connected 

 with an electro-magnet fixed to the base of the register, 

 and this again with the seismoscope, and, when the 

 circuit is closed during the occurrence of an carthqu.ike, 

 the pen is slightly, displaced to one side, and the record 

 of a shock consists of a notch in an otherwise uniform 

 line. Tlie paper is marked with lines corresponding 

 to intervals of five minutes, but, as the clock which 

 drives the cylinder cannot be depended on for keeping 

 accurate time, the electro-magnet is also connected 

 with a good pendulum clock so adapted that the circuit 

 is closed momentarilv once everv five minutes. "The 

 record of an earthquake," Professor Marvin remarks, 

 " consists of a succession, more or less prolonged, of 

 lateral jogs or strokes on the line traced by the pen. 

 whereas the clock record consists of a single stroke 

 occurring regularly and of very short duration." The 

 paper is dri\en at the rate of 2', inches an hour, and it 

 is thus not difficult to determine the time of a shock to 

 within a quarter or half a minute. 



Agamennones Seismoscope, 



.At first sight, there is some resenihl.nice hot ween Dr. 

 .Agamennone's seismoscope and Professor Marvin's. 

 The principal difference lies in the fact that the per- 

 forated plate is itself movable and magnifies the ori- 

 ginal displacenient of the ground. The seismoscope 

 is thus doubly sensitive. It is used chiefiy in Italian 

 observ.'itories, but is also to be found in Ilimgary, 

 Roumania, Bulgaria, India, the Dutch Indies, etc. 



The base .A of the instrument (fig. .}.) is a cin-ul.-ir 

 plate of cast iron, standing on three equidistant feet, 

 two of which arc levelling screws. Three vertical rods, 

 B, C, and D, rise upwards from three points of the 

 base which form the angular points of an equilateral 

 triangle. Tlie rcxl B is made f>f stwl, and is about 74 

 inches long, the lower part. 2! inches in length, being 

 a thick steel wire, and the upper portion a fine steel 

 rod, Tj'jth of an inch in diameter, .'md ending at the lip 

 in a short platinum wire. .A lens-sh;iped disc of lead K, 

 weighing a little less than half-a-pound, is fixed by a 

 screw to the rod B near its lower end. 'ITie second 

 rod C is of twice the thickness of the other, and of 

 about the same length, and carries at its upper end a 

 similar disc of lead F, fixed to it by a .screw. To this 

 disc is attached a small horizontal plate of platinum O. 

 perforated by a small round hole and so adjusted that 



