38 REPORTS ON THE STATE OP SCIENCE. 



given year represent an increase or decrease in activity, I have com- 

 pared such numbers with the average number which took place in a 

 certain period of years. The first average taken for all districts is for 

 the years 1700 to 1734. For Italy this, for example, is found to be 

 1'7 per year. Any year during which more than two large earthquakes 

 were noted is therefore a year in which seismic activity has been above 

 the average. The remaining periods are each of thirty-three years, 

 and respectively end in the year 1767, 1800, 1S33, 1866, and 1899. 

 The years in which these four widely separated districts, A, B, 0, and 

 D, have shown abnormal activity are the following: 1720, 1730, 1731, 

 1732, 1746, 1751, 1755, 1785, 1822, 1831, 1853, and 1885 (twelve 

 times). There was comparative quiescence for all four districts in the 

 years 1704, 1708, 1710, 1744, 1745, 1757, 1758, 1761, 1837, 1843, 

 1848, 1877, 1890, 1896, and 1899 (fifteen times). 



Three districts have shown unusual activity, while there has been 

 comparative quiescence in one in the following years: 1700, 1703, 

 1705, 1707, 1714, 1716, 1718, 1719, 1725, 1736, 1739, 1740, 1743, 

 1752, 1753, 1756, 1762, 1782, 1787, 1791, 1794, 1797, 1806, 1809, 

 1812, 1818, 1819, 1821, 1827, 1828, 1829, 1830, 1834, 1852, 1857, 

 1861, 1862, 1864, 1865, 1866, 1874, 1875, 1887, 1889, 1893, 1894 

 (forty-six times). 



Three districts have shown unusual quiescence while there 

 has been comparative activity in one, in the following years: 1701, 

 17U9, 1712, 1728, 1733, 1734, 1737, 1738, 1741, 1748, 1750, 1760, 

 1764, 1768, 1769, 1770, 1772, 1773, 1777, 1778, 1781, 1788, 179::, 

 1798, 1799, 1801, 1803, 1804, 1805, 1807, 1810, 1813, 1816, 1817, 

 1820, 1823, 1824, 1835, 1836, 1838, 1839, 1S40, 1841, 1844, 1845, 

 1851, 1860, 1863, 1867, 1869, 1879, 1880, 1883, 1884, 1886, 1895, 

 1897, and 1898 (fifty-eight times). 



In all other years between 1700 and 1899 two districts have been 

 active and two districts have been quiescent. 



If the seismic activity or quiescence of three large districts out of 

 four in the world is an indication that there has been unusual seismic 

 activity or quiescence in the world generally, then the last two tables 

 may be taken in conjunction with the two first. If we do this we see 

 that, in 131 years out of 200, seismic activity or quiescence has 

 generally been simultaneously in accordance in various parts of the 

 world. In the remaining sixty-nine years the activity of two large 

 districts has been balanced by the quiescence in two other large 

 districts. 



' V. Megaseismic Frequency. 



Between 1899 and 1909 the number of very large earthquakes 

 recorded was not less than 976. Many of these were recorded at 

 stations all over the world, others over the whole of the Northern 

 Hemisphere, and none of them disturbed an area less than that of 

 Europe and Asia. 



