﻿234 Scientific Intelligence. 



8,000 and 9,000 and fifteen between 5,000 and 8,000. Mr. Milne 

 ascended Oshima, an active volcano on the island of that name 

 (height 2,500 feet) in May, 1877, after an eruption which com- 

 menced on the 4th of January. The interesting points are that 

 the eruption began with only a very slight vibration or earth- 

 quake; the slope on the side ascended was 40° to 50° ; explosions 

 within were heard before reaching the top, which were afterward 

 found, when at the top, to occur in succession every two seconds, 

 with occasional pauses, and to be due to successive outbursts of 

 steam, each producing a throw upward of ashes and bombs some- 

 times nearly to a height of 1,000 feet ; the fragments fell verti- 

 cally or nearly so unless wafted by the winds. The walls of the 

 crater were vertical and about 300 feet in height. The volcano 

 Asamayama, 8,800 feet high (p. 95), is said to break forth in 

 eruption after it has become clogged by depositions of sulphur ; 

 but some source of action within must be the real cause of its 

 periods of activity. 



The number of volcanoes, easily recognized as such by their 

 cones, is 129, and of this number 51 are still active; 16 of the 

 active are in the Kuriles, 11 in Yezo, and 24 in the central and 

 southern region. Records of 233 eruptions are reported by Mr. 

 Milne (some dating back of the Christian era) ; 32 of them in the 

 northern district, 63 in the central, and 138 in the southern. Of 

 those whose month of outbreak is known — 153 in number — 80 oc- 

 curred in the winter months and 73 in the summer; and the 

 largest number in the months of February and April. The erup- 

 tions hence follow, says Mr. Milne, the same law as the earth- 

 quakes : " During the winter months the average barometric 

 gradient is steeper than in summer ; and this, with the piling of 

 snows in winter, gives rise to long continued stresses, in conse- 

 quence of which certain lines of weakness in the earth's crust are 

 more prepared to give way during the winter months than they 

 are in summer." 



The lavas consist mostly of augite-andesite ; but those of Fuji- 

 san, Oshima, and Hakone are basic and like basalts, giving for 

 the silica 49 to 52 per cent, with nearly 10 per cent of iron ox- 

 ides. The rocks are strongly magnetic, and some pieces have 

 been noticed to be polar. Dr. E. Naumann states in a paper in a 

 volume of the Seismological Journal of Japan, that near Ganju-san, 

 for some unexplained reason, the magnetic declination has in the 

 last eighty years decreased 19°, changing in that time from 14° 

 30' JE. to 5° W.; and that the change is less as you recede from 

 the mountain. Such a fact, says Mr. Milne, makes frequent ob- 

 servations desirable about the large volcanoes that lie in the track 

 of vessels. 



Mr. Milne discusses the forms of volcanoes, in continuation of 

 former observations referred to by Mr. Becker in his paper in 

 volume xxx (1885, p. 283) of this Journal. The principle dis- 

 cussed by these authors has reference especially to one of the 

 conditions on which form depends — the resistance to crushing, 



