amined a large number of barographs, from which he has been able to fix the dates at which the atmospheric undulations passed various places on the earth's surface. As in the sea, so in the air, two waves, one to the east and one to the west, started from Krakatau, whose rate of progress has been found to be that of sound. One surprising circumstance, of which we have as yet observed no explanation, is how those ships which were near the volcano at the moment of the supreme explosions, of the enormity of which they seem not to have been cognizant, notwithstanding that they were heard at such immense distances, did not only not suffer from the concussion, but were not blown off the face of the water altogether. Almost coincident with the record of the abnormal atmospheric fluctuations, magnificent sunlight effects, unusually lurid skies, prolonged dawns, lengthened twilights, and green or blue or moon-like suns, began to be observed. From the dates at which these phenomena first appeared in different parts of the world—on the east coast of Africa on the second day, the Gold Coast on the third, Trinidad on the sixth day, at four thousand miles in the Pacific west of Panama on the seventh, and at Honolulu on the ninth day—it can be seen that the volcanic cloud followed a straight path.
To what height the supreme outburst propelled the smoke, dust, and the lighter portion of matter, it is impossible at present to estimate. Mr. Whymper saw Cotopaxi, in by no means one of its extraordinary expirations, eject a column over 20,000 feet in height; but many multiples of this distance will doubtless be required to measure the spire that was shot sky-ward on the forenoon of the 27th of August last. At all events it rose so high that months have been required for it to descend. Those places situated below the direct westward path of the cloud, which would be elevated at first as a narrow column, as they were carried under it by the eastward rotation of the earth, were the first to have the usual light of the sun changed into ominous displays or delightful after-glows, varying in intensity according to their time-distance away, and therefore to the amount of the obstructing dust, which would also condense moisture in the upper part of the air, and give special absorption effects,[1] that had by the hour they were reached subsided from the atmosphere. This narrow band, gradually spreading out north and south, enabled the inhabitants of all lands to obtain a view of the gorgeous effects of broken and absorbed sunbeams, and a demonstration of the vastness of the power of imprisoned steam.
Many questions connected with the subject remain at present unexplained; but the difficulties will in great part doubtless disappear before our fuller information. A committee of the Royal Society, consisting of our highest authorities in meteorological, volcanic, and light phenomena, has, as we have said, been appointed to fully investi-
- ↑ Cf. "Nature," February 21, 1884, pp. 381, 882.
