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The island of Hawaii, or the most recent and easterly, is composed of four mountains-the Mauna Kea, 14,500; Mauna Loa, 13,800, Huallalei, 8000, and Kohala, about 5000 feet in height, with large valleys of 2000, 3000, to 6000 feet above the sea-level between. The slope of the mountains is usually gentle, and numerous small craters of 100 to 300 feet in height are found distributed on their sides, and also in the intermediate valleys. On the west side precipitous rocks face the sea, with a height of 3000 feet, which have valleys opening seawards that are almost inaccessible from the land side, owing to the precipitous character of their sides. It is on this island that the most recent displays of volcanic activity are seen, the country having been overrun in many places by lava flows, which have left large tracks quite useless for agricultural purposes. Earthquakes are common, and the summit crater of Mauna Loa, 13,800 feet up, is frequently, and that of Killauea (on a level plateau on the side of Mauna Loa, about 3000 feet above the sea) is almost always in a state of activity. The crater of Killauea is on the north-east of Hawaii, about 32 miles from the bay of Hilo, which is the most convenient starting-point for those wishing to visit the volcano. In the ride of 32 miles one has an ascent of some 3000 feet, but the ups and downs are so numerous that one can hardly detect it. During some portion of the way one passes through very dense tropical vegetation, palms, tree ferns, &c., with creepers and ferns clustering around, but for the most part the path lies over lava flows, so recent as to be almost devoid of vegetation, which render it so rugged as to compel one to walk his horse the greater part of the way. When approaching the volcano the visitor is at first struck by the sight of hundreds of steam jets rushing up in all directions, some of which are utilised as vapour baths, by putting a wooden box over them with a hole in the top large enough to admit the neck of the bather. On going some hundred yards further, an immense pit appears, at the further end of which during the day are seen large volumes of smoke, while at night a red flare is visible in the sky, with an occasional piece of white hot lava getting tossed up high enough to be seen above the edge of the inner crater. This large pit or outer crater is of oval shape, and some 3 miles long by 14 to 1 mile broad in the widest part. The sides are precipitous, and from 600 to 700

feet in height, being in many places divided into close parallel ridges, showing the height to which the lava had reached before breaking out at a lower level. There were two large sulphur beds at the side of the outer crater, about 2 miles distant from each other, and pieces of native sulphur could be picked up, each with a hole in its centre, showing that the vapour had solidified round the hole from which it had emerged. The floor of the outer crater was composed of black lava, several acres of which were covered over one night by the lava breaking out at a side of the lowermost edge of the outer crater, quite distant from the inner one.

Our first descent was made at night by means of some rustic staircases cut in the sides of the ridges, and assisted by whatever brushwood might be growing on the sides. At last our party were landed on a floor of black lava, all seamed with cracks and contorted into curious shapes, sometimes like a mass of cable ropes mingled together, at others showing large pudding-like excrescences, which are dangerous to walk upon, since they are simply large bubbles with a thin covering, to guard against which each visitor carries a thick stick wherewith to test the ground before him.

After walking for about half an hour on this black lava, and crossing innumerable cracks of from three inches to a foot in width, some of which showed a white line of fire about 6 feet beneath, the gradual ascent to the inner crater was reached. Its position in regard to the general form of the outer crater may be said to be in one of its foci, and its size, by estimation, about a mile long by broad. The increasing glare and smoke now warned us of our proximity to the more active parts, while here and there on the outer side of the inner crater were some bright red streaks, which, on our closer approach, turned out to be red hot lava flowing through holes in the outer side of the inner crater on to the general surface of the outer one.

The ascent of some 70 feet to the top of the inner crater is a gradual one, and considerable detours had to be taken to get round the parts which were being overflowed. The lava of its sides was twisted about and broken up in a most ugly manner, besides being so rotten as to break away in flakes whenever a foot was put upon it. The greatest caution was needed to test the ground before treading on it, and frequent play had to be made with our thick

sticks. Tumbles were frequent, from which the writer escaped unharmed by having a thick pair of dogskin gloves on his hands. One of our party, however, a professor from Indiana, managed to fall into a crack up to his middle, and got his hands severely cut

and burnt.

The view from the top, however, amply repaid the trouble. Four lakes of molten lava, the largest some 200 yards in length, and of kidney shape, and the others of smaller size, were seen in full activity. In the largest lake seven to eight fountains of white hot lava were playing up at once to a height of 30 to 40 feet, one sometimes stopping and another commencing at a different part of the side of the lake.

The lava in this lake was about 50 feet below the inner edge of the crater, and appeared to be slowly advancing toward the tunnels from which we had seen it issuing on the road up. The lakes were not at the same level, and you might see one brimful and another 60 to 70 yards off at a level of some 30 or 40 feet below it. On another of the lakes, about 50 yards wide, was a single fountain, bursting from a cavern in its side, and throwing lava half-way across its surface, while from the roof and sides of the cavern hung down lava stalactites.

After looking at this for some time, the claims of our injured friend became so strong, as to oblige us to take him back to the crater house, resolved next day to have a more deliberate inspection.

The next day proved wet, but the writer explored his way through the driving mist formed by the rain coming in contact with the heated lava, the only disagreeable incident being his getting to the leeward of a blow-hole, and having to run to get clear of the suffocating sulphur vapours. This blow-hole was about the size of a man's body, and as you went forward to it you heard a gurgling sound beneath. Smoke was coming out in considerable volumes, and on looking in, the sides were seen to enlarge beneath and be at a white heat.

Having at length got seated comfortably upon an upheaved block of lava about 20 feet above the larger lake, and 8 to 10 yards from its side, a new fountain sprung up suddenly from the side of the lake quite close at hand, which immediately forced a retreat to

a more respectful distance. About the same number of fountains continued to play up as on the preceding evening, and looked red by day. Daylight, however, drowned out the redness of the lakes. as seen by night, and made them appear quite black.

After watching for a considerable time, a red hot crack was seen to start suddenly from one side of the lake to the other, then other cracks in different directions, and first one-half of the lake and then the other was covered with a fresh coating of red hot lava, the former tumbling out of sight as it got shrunk and cracked in cooling.

A curiosity called Pele's hair is found round the sides of these lakes. This is composed of fine fibres of lava cooled, broken off from the molten liquid while being spouted up in the fountains, carried away by the wind, and lodged in the cracks around.

The summit crater of Mauna Loa, some 15 miles off, and 10,000 feet above Killauea, was in activity about a month previous to our visit to the island, but limited time prevented our seeing it. Some points of curiosity may be noted before ending.

1. The lakes are not at the same level, although quite close to each other.

2. The summit crater of Mauna Loa is 10,000 feet above Killauea, and frequently in violent eruption, while Killauea is comparatively undisturbed.

3. The outer crater of Killauea appeared to act as a receptacle for the lava, which, as soon as it arrived at a sufficient height, and got the assistance of an earthquake, broke through below and covered the country, sometimes running in a broad stream for 25 miles, and leaving an indication of the level which it had reached in form of a new ridge within the lip of the outer crater.

4. The necessity of an earthquake to enable it to break through is shown by the great difference of heights of the lava even within short distances.

5. The fountains were in every case playing round the edges of the lakes.

5. New General Formulæ for the Transformation of Infinite Series into continued Fractions. By Thomas Muir, M.A.

The name of the Hawaiian Fire-Goddess.

6. Laboratory Notes. By Professor Tait.

(a) On a Possible Influence of Magnetism on the Absorption of Light, and some correlated subjects.

Professor G. Forbes' paper, read at a late meeting of the Society, and some remarks made upon it by Professor Clerk-Maxwell, have once more recalled to me an experiment which I tried for the first time rather more than twenty years ago, in Queen's College, Belfast. I have since that time tried it again and again, whenever I succeeded in getting improved diamagnetics, a more powerful field of magnetic force, or a more powerful spectroscope. Hitherto it has led to no result, but it cannot yet be said to have been fairly tried. I mention it now because I may thus possibly be enabled to get a medium thoroughly suitable for a proper trial.

The idea is briefly this,―The explanation of Faraday's rotation of the plane of polarization of light by a transparent diamagnetic requires, as shown by Thomson, molecular rotation of the luminiferous medium. The plane polarized ray is broken up, while in the medium, into its circularly-polarized components, one of which rotates with the ether so as to have its period accelerated, the other against it in a retarded period. Now, suppose the medium to absorb one definite wave-length only, then-if the absorption is not interfered with by the magnetic action-the portion absorbed in one ray will be of a shorter, in the other of a longer, period than if there had been no magnetic force; and thus, what was originally a single dark absorption line might become a double line, the components being less dark than the single one.

Other allied forms of experiment connected with this subject were discussed.

(b) On a Mechanism for Integrating the General Linear Differential Equation of the Second Order.

I am anxious to explain to the Society a kinematical device for the solution of the General Linear Differential Equation of the Second Order before I become acquainted with the principle of the integrating machine which, I understand, was described last Thursday by our President to the Royal Society.

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