548 



NATURE 



[Feb. 9, 1^88 



some violence and oscillation due to their momentum ; 

 but those inside the contour A B c D will continue moving 

 for a little longer. The outside layer of this region will 

 slip in such direction as to illustrate the direct induced 

 current at " break," and will begin to stop first ; tfee slip 

 and the stop gradually penetrating inwards, just as 

 happened during the inverse process, until all trace of 

 rotation ceases. This inverse slipping process is the 

 direct induced current at " break." 



Through a perfect conductor the disturbance could 

 never pass, for the slip of the dielectric wheels on its 

 outer skin would be perfect, and would never penetrate 

 any deeper. A superficial current lasting for ever, or 

 rather as long as the magnetic field (the rotation of the 

 dielectric wheels) lasts, is all that would be excited, and 

 it would be a perfect magnetic screen to any dielectric 

 beyond and inclosed by it. Oliver J. Lodge. 



( To be cojittnued.) 



THE BIRDS'-NEST OR ELEPHANT ISLANDS 

 OF THE MERGUI ARCHIPELAGO. 



r\^ the geological structure of this group of islands 

 ^^ lying off the coast of British Burmah not much is 

 yet known. Our readers will probably be interested in 

 the following account of a visit to one portion of the 

 archipelago, furnished by Commander Carpenter, R.N., 

 to the Hydrographer of the Admiralty, to whose kindness 

 we are indebted for permission to publish it. 



The remarkable group of islands called by the Burmans 

 Ye-ei-gnet-thaik (///. sea-birds' nests) is located on the 

 south-east side of Domel Island, one of the largest of the 

 Mergui Archipelago. It is composed of six marble rocks, 

 the highest and largest of which, looo feet in altitude, and 

 about one mile in length, is oval-shaped, and rises very 

 abruptly out of a depth of only 5 fathoms. The islands 

 present a very striking appearance, particularly if the 

 ■weather is hazy, when they are not seen until within five 

 or six miles, for then they gradually loom out through the 

 mist like some huge misshapen monsters that have strayed 

 away from civilization. Their sides are partly clothed 

 with vegetation wherever a break in the limestone has left 

 a cleft in which moisture and dust can lodge. Conspicuous 

 because of its leaning attitudes is a species of tree-fern 

 which grows at any angle, but only above a height of 200 

 feet from the water. The face of the rocks is reddish, 

 partly from weathering and partly from soil, and where 

 cliffs exist the most beautiful though uncouth stalactites 

 have been formed, showing grotesque and snake-like 

 patterns varying in hue and shape till one feels as if in 

 some enchanted land. But the great feature of the group 

 is the birds'-nest caverns, which as a rule open into the 

 sea, the entrance being below high-water mark ; fortun- 

 ately I visited them at spring tides, and had plenty of 

 leisure to examine each cavern at low water during two 

 days. 



At the south end of the largest island stands a " nine- 

 pin " of gray marble 370 feet high, almost separated from 

 the rest. It is hollow, like a huge extinguisher, and the 

 polished light-blue and yellow sides of the interior seem 

 to point to its having been hollowed by the swell of the 

 sea, which on entering the cave would probably expend its 

 force vertically, the mouth of the cave being open to the 

 direction of the strongest seas. This sea-stack forms the 

 western point of a nearly circular cove, 360 yards in 

 diameter, which runs back into the island, and the sides 

 of the cove rise steeply though not perpendicularly from 

 it. At the head of the cove is a perpendicular wall of rock 

 over which can just be seen the 1000-foot summit in the 

 distance. 



At half-tide a tunnel, passable for a canoe, opens under 

 the wall of rock at the head of the cove, but a ship's gig 

 can only enter within an hour of low-water spring tides. 



This tunnel has a roof covered with large stalactitic knobs 

 except at its narrowest part, where it is apparently scoured 

 smooth by the action of the tidal rush. It is about 250 

 feet long, and 4 feet deep at low water (the rise and fall 

 of the tide being 16 feet), and is covered with dripping 

 marine life, corallines, small corals, Comatulae, sponges, 

 and sea-horses. Passing through this submarine passage 

 one emerges into another circular crater-shaped basin 

 with perpendicular sides. This basin is only open to the 

 sky ; caves here and there enter it, some of which may 

 perhaps lead by long tunnels to other basins. Water was 

 running freely into it from the foot of the cliffs in several 

 places as the tide fell, showing that water spaces existed, 

 and strange gurgling sounds as of air taking the place of 

 water could be heard now and again. There were hardly 

 any signs of the place being frequented by man except 

 here and there the worn ropes of birds'-nest climbers. It 

 was either not the season for the swallows or they had 

 deserted the islands, for none were seen. A little red- 

 dish guano was noticed in some of the caves. There 

 can be but little traffic through the tunnel by which we 

 entered, for the delicate growth on its sides was hardly 

 injured. 



On the west side of the northern large island a lofty 

 cavern is connected at half-tide with another nearly 

 circular basin of about the same size as that we have just 

 described, but in this case the basin also opens into the 

 sea on the east side of the island. After contemplating 

 the cliffs that surround these basins, the general cir- 

 cular contour of the ridges of the islands, the under- 

 mining action of the sea at the water-line, which causes in 

 some places an overhang of 20 to 25 feet, and the softening 

 of the marble surface of the cavern roofs by moisture, the 

 conviction gradually forces itself on the mind that these 

 circular basins were themselves at one time the floors of 

 huge caverns ; that in days gone by the islands rose far 

 higher, with cavern piled on cavern, and that the work of 

 disintegration by solution and wave action is slowly 

 going on, pulling down these marble monuments of a 

 giant age. Indeed, here and there a fall of blocks has 

 occurred lately, and, as there is no shoal off the base of 

 the slip, the destructive action is probably rapid. 



A small oyster covers the rocks at the water-line. A 

 handsome kingfisher was secured and sent to the British 

 Museum. A few doves and an eagle or two were the only 

 other birds seen, besides a small bat in the caves. By 

 the position of the nest-seekers' ropes, the swallows 

 appear to build only on the roofs of the caves. The 

 islands appeared to be entirely composed of a blue-tinted 

 marble. A vessel could lie alongside them and lower the 

 cut blocks straight into her hold, but it is probably of too 

 poor a quality to be worth shipment. 



Alfred Carpenter. 



PRIZE FOR RESEARCHES IN NATURAL 

 HISTORY. 



IN accordance with the intentions of the founder, the 

 Committee of Schnyder of Wartensee's Foundation, 

 Zurich, have decided to offer for the year 1890 a prize for 

 the following researches in natural history : — 



" New investigations are desired regarding the relation 

 which the formation of the bones bears to the statics and 

 mechanics of the vertebrate skeleton. The results of the 

 investigations as a whole are to be demonstrated in 

 detail by way of example on the skeleton of a definite 

 species." 



The conditions are as follow : — • 



Art. I. Competitors for the prize must send in their 

 work in German, F>ench, or English, by September 30, 

 1890, at the latest, to the address given below in Art. 6. 



Art. 2. The award will be made by a Committee con- 

 sisting of the following gentlemen : — Prof. Hermann von 



