Seismograph
2 of the 6 encyclopedias on this shelf carry an entry for Seismograph. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a seismometer; an instrument for recording the period, exeach of the vibratent, and direction of tions which constitute an earthquake. For a complete seismography, three distinct sets of apparatus are required: (1) To record horizontal motion; (2) to record vertical motion; and (3) to record time. The horizontal and vertical motions must be written on the same receiver, and if possible side by side, while at the instant at which the time is recorded a mark must be made on the diagram which is being drawn by the seismograph. The first instruments were merely modifications of the seismoscope, but successive improvements have been introduced, and the seismograph has been brought to a high pitch of perfection. Some of the best, if not the best forms known are in use in the Imperial Observatory at Tokio, Japan.
Aiton's Encyclopedia (1910)
sismo-graf, an instrument designed to record an earthquake shock. The simplest contrivance is a cup of molasses. The wave of molasses raised by the quake registers itself by a stain on the side of the cup. The scientific instrument, known also as seismometer (sis), registers by means of three delicate pointers tracing lines on smoked glass. A tremor of the earth starts clockwork that sets the panes of glass in motion. One of these pointers points in a vertical direction, the others are horizontal. The direction, violence, and duration of the motion is indicated by lines traced on the glass. An ingenious contrivance causes a clock to stop at the beginning of the tremor, thus fixing the time of occurrence. The Japanese excel in the study of earthquakes by means of these instruments.
What Has Changed in the Last Century
The mechanical instruments described here — Aiton's 1910 pointers scratching smoked glass, Collier's three-part apparatus of 1921 — have been wholly superseded by electromagnetic and broadband digital sensors that transmit data continuously to computers, with hundreds of stations in the Global Seismographic Network and thousands more worldwide. What changed most is what the records were used for: Andrija Mohorovicic identified the crust-mantle boundary from seismograms in 1909, Beno Gutenberg fixed the depth of the core in 1913, and Inge Lehmann deduced the solid inner core in 1936 — the instrument became the chief tool for mapping the Earth's interior, not merely for logging shocks. Charles Richter's magnitude scale of 1935, later replaced for large events by the moment magnitude scale, gave the readings a number the public could use. Collier's praise of the Imperial Observatory at Tokyo still holds in spirit: Japan operates one of the densest seismic networks on Earth, feeding an earthquake early-warning system that has run nationwide since 2007.
Written for this edition, 2026.