Two Heavy Seismographs

Abstract

TWO new seismographs devised by Dr. Wiechert are now on sale by Spindler and Hoyer, of Göttingen. The fact which will strike most seismologists is the magnitude of the “stationary” are employed. The horizontal pendulum uses a “stationary” mass of 17,000 kilo., nearly 17 tons. The mass is composed of barytes contained is a cylindrical sheet-iron vessel with a flat bottom. Its dimensions are 2 metres in diameter by nearly 2 metres in htight, and, being intended to have freedom of movement horizontally, the vessel is suspended by three iron rods of 3 cm. diameter, the elasticity of which allows the necessary freedom. The next striking feature is the multiplication with which the thrust arm moves the indicator point, and this is 2200! It is brought about by means of four levers, multiplying 5X5X5X17½. The loss owing to the inertia and elasticity of the connecting system amounts to 5 per cent. only. “The instrument renders specially important service in the small European earthquakes where the rapid oscillations are more prominent.” It is clear that this statement is justified. For local disturbances and extremely rapid elastic vibrations the instrument should be of great service, but, with such a multiplication, one is compelled to wonder how much the machine requires to be isolated in order to avoid the disturbance due to traffic. It is not surprising to find in a specimen seismogram tremors due to a gas engine 2½ kilometres distant. Other drawbacks to the use of the pendulum are the price, 5000 marks, and the number of times the paper must require to be changed. These purely practical considerations must have weight with anyone who has real work in view.