Paradoxical as it appears, the sound was sometimes better heard in distant places than in those nearer the seat of disturbance. This singular effect has been thus explained—assuming, for example, the presence of a thick cloud of ashes between Krakatoa and Anjer, this would act on the sound-waves like a thick soft cushion; along and above such an ash-cloud the sound would be very easily propelled to more remote places, for instance, Batavia; whereas at Anjer, close behind the ash-cloud, no sounds, or only faint ones, would be heard. Other explanations seem to be less probable, though not impossible. Dr Verbeek states that within a circle of nine and a-half miles’ radius (fifteen kilomètres) from the mountain, the layers of volcanic ash cover the ground to a depth of from sixty-five to one hundred and thirty feet, and at the back of the island the thickness of the ash-mountains is in some places even from one hundred and ninety-five to two hundred and sixty feet, and that the matter so projected extends over a known area of seven hundred and fifty thousand square kilomètres (285,170 square miles), or a space larger than the German Empire with the Netherlands and Belgium, including Denmark and Iceland, or nearly twenty-one times the size of the Netherlands. Moreover, he calculates that the quantity of solid substance ejected by the volcano was eighteen cubic kilomètres, or 4.14 _cubic miles_. To give some idea of the enormous volume this represents, we may take the following illustration: the largest of the Egyptian pyramids has upwards of eighty-two millions of cubic feet of masonry; it would therefore take about _seven thousand three hundred and sixty of such structures_ to equal the bulk of matter thrown out by this eruption. Some of this matter was found to contain smooth round balls from five-eighths to two and a-quarter inches in diameter, and composed of fifty-five per cent. of carbonate of lime. As may well be imagined, the final outburst by its awful energy gave rise to a succession of air-waves. These we now know went round the earth more than once, and recorded themselves on the registering barometers or barograms at the Mauritius, Berlin, Rome, St Petersburg, Valencia, Coimbra (Portugal), and other far-distant places. At some points, as many as seven such disturbances were noted; other instruments not so sensitive gave evidence of five, by which time the wave had pretty well spent itself.