Earthquakes have been made to yield testimony of the most striking character with regard to the rigidity of the earth. The researches we are now to describe are mainly due to Professor Milne, who, having enjoyed the advantage of studying earthquakes in their natural home in Japan, where are to be found some of the most earthquake-shaken regions of this earth, has now transferred his observations of these phenomena to the more peaceful regions of the Isle of Wight. But though the Isle of Wight is perhaps one of the last places in the world to which anyone who desired to experience violent earthquake shocks would be likely to go, yet by the help of a beautiful apparatus Professor Milne is actually able to witness important earthquakes that are happening all over the world. He has a demonstration of these earthquakes in the indications of an extremely sensitive instrument which he has erected in his home at Shide. When our earth is shaken by one of those occasional adjustments of the crust which I have described, the wave that spreads like a pulsation from the centre of agitation extends all over our globe and, indeed I may say, is transmitted right through it. At the surface lying immediately over the centre of disturbance there will be a violent shock. In the surrounding country, and often over great distances, the earthquake may also be powerful enough to produce destructive effects. The convulsion may also be manifested over a far larger area of country in a way which makes the shock to be felt, though the damage wrought may not be appreciable. But beyond a limited distance from the centre of the agitation the earthquake will produce no destructive effects upon buildings, and will not even cause vibrations that would be appreciable to ordinary observation. This earth of ours may transmit from an earthquake pulses of a very distinct and definite character, which are too weak to be perceived by our unaided senses; but, just as the microscope will render objects visible which are too minute to be perceived without this aid to the ordinary vision, so these faint earth-pulses may be rendered perceptible by the delicate indications of an instrument which perceives and records tremors that would pass unnoticed by our ordinary observations. The ingenious instrument for studying earthquakes is called a seismometer. It marks on a revolving drum of paper the particulars of those infinitesimal tremors by which the earth is almost daily agitated in one place or another.