The nearest place at which good time-observations were made is Calcutta, distant 255.5 miles from the assumed centre. One is indicated on the recording tide-gauge by a sudden rise of the water, while the others were obtained from the central telegraph office, the terminal railway stations, and from two careful readings by interested observers. They vary from 4h. 27m. 0s. to 4h. 28m. 37s. P.M., all being liable to an error of half-a-minute. The arithmetic mean for the beginning of the shock is 4h. 27m. 49s., and this is probably as accurate an estimate as the conditions allow.[70] Bombay lies outside the disturbed area, 1208.3 miles from the equivalent centre; and, for the time of arrival in that city, we have to depend on the records of the barograph and the three magnetographs. The horizontal force magnet was set in motion two and a half minutes before the others, no doubt by the advance tremors. The times given by the barograph and the vertical force-instrument differ by only one minute, and the best result seems to be that obtained by taking their mean--namely, 4h. 35m. 43s., which is probably accurate to within a minute. Assuming, then, that the time-interval between Calcutta and Bombay does not err by more than half-a-minute, it follows that the intervening velocity must lie between 2.8 and 3.2 kilometres per second, its probable value being 3 kilometres, or 2 miles, per second. The remaining records, which are of less value than those obtained in these cities, fall into two groups, the first consisting of a number of stations along a line running north and south between Calcutta and Darjiling or within a hundred miles on either side of the same, and the second a long series of stations crossing Northern India in a nearly westerly direction. The observations made at the Burmese stations were unfortunately affected by an error arising from the retardation of the Madras time-signals through frequent repetition along the line. [Illustration: FIG. 70.--Time-curve of Indian earthquake. (_Oldham._)]