The explosion which occurred in East London at 6.51 p.m. on January 19, 1917, was one of the greatest ever experienced in this country. The sitex of the explosion is indicated approximately by the star in the accompanying maps. The total amount of explosives lost is known, if at all, only to those in authority.

In order to determine the forms of the sound-areas, I wrote letters to most of the principal newspapers published in London and within and near the districts concerned, and I am greatly indebted to the courtesy of many editors in allowing me space for which there were so many important claims, and also to the numerous correspondents who so kindly answered my inquiries. After the boundaries of the sound-areas had been drawn from an unusually large number of positive records, I wrote to the incumbents of many parishes in small towns and large villages, and to superintendents of police within the silent zone and just within and for some distance outside the boundaries of the sound-areas as I had drawn them. The total number of positive records is 571 from 391 places, and of negative records 75 from 71 places. In addition to these, there are 79 records from 71 places at which the sound was apparently not observed, but at which windows were shaken or pheasants disturbed; making a total of 725 records from 533 places.