492 



NATURE 



\Marck 27, 1890 



bach, of Basle, showed some photographs of cirrus clouds 

 taken by reflection from the surface of the Lake of 

 Sarnen. In this case the surface of the water acts like 

 a polarizing mirror, and extinguishes the skylight. Photo- 

 graphs of clouds were also exhibited by Mr. Clayden, 

 Dr. Drewitt, Dr. Green, Mr. Gwilliam, Mr. Harrison, 

 Mr. McKean, Messrs. Norman May and Co., Mr. H. C. 

 Russell, and Mr. Symons. Mr. H. P. Curtis, of Boston, 

 U.S.A., sent a valuable and highly interesting collection 

 of photographs, showing the devastation caused by the 

 tornadoes at Rochester, Minnesota, on August 21, 1883, 

 and at Grinnell, Iowa, on June 17, 1884. After seeing 

 these photographs, some idea can be formed of the 

 immense destruction wrought by these terrible scourges, 

 which so frequently visit various parts of the United 

 States. Mr. Curtis also exhibited three photographs of 

 the tornado cloud ; two of these were taken at James- 

 town, Dakota, on June 6, 1887, when the cloud funnel 

 was 12 miles to the north ; the third, which was taken 

 in New Hampshire, during the storm on June 22, 1888, 

 shows the spiral-shaped funnel trailing at a considerable 

 altitude in the air. 



Many interesting photographs illustrating meteoro- 

 logical phenomena were exhibited. These included floods, 

 snow-drifts, hoar-frost, frozen waterfalls, &c. A large 

 number of photographs of flashes of lightning taken 

 during the last twelve months were also shown, as well 

 as some photographs of electric sparks, taken by Mr. 

 Clayden and Mr. Bidwell, which explain the formation 

 of dark images of lightning-flashes. 



Mr. Clayden exhibited a very interesting and instruc- 

 tive working model, showing the connection between the 

 monsoons and the currents of the Arabian Sea and the 

 Bay of Bengal. 



Mr. Dines showed a model of the whirling machine 

 used by him at Hersham for testing anemometers and 

 for experiments on wind-pressure ; he also exhibited a 

 remarkable curve showing the normal component of the 

 wind-pressure upon a sloping surface i foot square, the 

 normal pressure being taken as 100, and the pressure at 

 various angles of inclination being expressed proportion- 

 ately. Mr. Munro sent two instruments which he has 

 recently constructed in conjunction with Mr. Dines. 

 The first is for showing the velocity of the wind. The 

 shaft of an anemometer is connected with the shaft of the 

 instrument, and in turning works a small centrifugal 

 pump, thus raising the level of the mercury in the long 

 cistern. The deflection of the pendulum from the vertical 

 position is proportional to the rate of turning, and thus 

 gives a uniform scale. The second instrument is for 

 showing the pressure of the wind from a velocity anemo- 

 meter. The arrangement is the same as in the preceding 

 instrument, but the fall of the float in the small circular 

 cistern is proportional to the square of the velocity and 

 therefore to the wind-pressure, thus giving a scale of 

 pressure with the divisions at uniform distances. 



Mr. Hicks exhibited Draper's self-recording metallic 

 thermometer ; a mercurial minimum thermometer with 

 lens front ; and a radial scale thermometer. Mr. Long 

 showed Trotter's compensating thermometer for taking 

 temperatures at any distance ; and Mr. Denton exhibited 

 his clinical thermometer case with new spring-catch. 



William Marriott. 



THE ORIGIN AND COMPOSITION OF THE 

 FLORA OF THE KEELING ISLANDS. 



A T intervals I have contributed to Nature the results 

 -^*- of the more recent investigations of insular floras, 

 more especially in relation to the dispersal of plants by 

 ocean currents, birds, and winds ; and now, through the 

 courtesy of the author and Captain Petrie, Honorary 

 Secretary of the Victoria Institute, I am able to furnish 



a commentative summary of a lecture^ by Dr. H. B. 

 Guppy, on the flora of the Keeling Islands. 



It is hardly necessary to mention that Darwin visited 

 these islands in 1836, except in connection with the fact 

 that Dr. Guppy's visit was in a measure an outcome of 

 that event. In 1878, Mr. H. O. Forbes spent some time 

 there, and extended our knowledge of the flora. Primarily, 

 no doubt, the coral-reef question took Dr. Guppy to the 

 scene of Darwin's early labours, though he was probably 

 not less interested in the flora, having been stimulated by 

 practical botanizing in the Solomon Islands a few years 

 previously ; and a stay of nearly ten weeks enabled him 

 to elucidate many points that were either obscure or 

 conjectural. 



Mr. John Murray, of the Challenger Expedition, found 

 funds for Dr. Guppy's mission, and he presented to the 

 Kew Herbarium the collections made of dried plants and 

 drifted seeds and fruits ; and there, such of them as were 

 not already familiar to Dr. Guppy, and of which the mate- 

 rial was sufficient, were named, and a set incorporated. 



For the sake of brevity it will be better to describe 

 what Dr. Guppy has accomplished, rather than follow 

 him through his account of it. 



Specimens were taken of all the different species of 

 plants found in a wild state in the islands ; notes made 

 of the conditions under which they occurred, of their 

 relative frequency, of their chances of propagation, and 

 of their natural enemies, besides other particulars. In 

 addition to seeds, or fruits containing the seeds, of the 

 plants actually established on the islands, many others 

 were picked up on the beach, where they had been de- 

 posited by the waves. Whilst most of these were in 

 various stages of decay, others were actually germinat- 

 ing, and the question arose. Why had they not succeeded 

 in obtaining a footing ? As we shall presently learn, this 

 question was easily answered. 



Another point on which we had little trustworthy in- 

 formation was the length of time various seeds of essen- 

 tially littoral and insular plants would bear immersion, 

 or, rather, flotation, in sea-water without losing their 

 vitality. With the exception of a few isolated instances 

 of seeds having germinated after having been carried 

 across the Atlantic to the western coast of Europe, very 

 little was known, because the majority of the seeds ex- 

 perimented with by botanists at home did not belong to 

 this class of widely-spread plants. Dr. Guppy instituted 

 experiments on the spot, and although his time was too 

 short to determine the extreme limits of endurance of 

 the various seeds, he was able to prove that certain kinds 

 germinated freely after being thirty, forty, or fifty days in 

 sea-water. Again, he observed that some seeds that do 

 not readily float, or only for quite short periods, are con- 

 veyed hither and thither in a variety of ways — such as in 

 the cavities of pumice-stone, and in the crevices of drift- 

 wood. 



From all available evidence, it is almost absolutely 

 certain that there were no permanent inhabitants of the 

 Keeling Islands till about the end of the first quarter of 

 the present century ; and from the most trustworthy ac- 

 counts the islands were covered with vegetation, the 

 coco-nut largely preponderating in the arboreous ele- 

 ment. Indeed, as the outer part was almost entirely 

 coco-nut, it seemed, as Darwin says, at first glance to 

 compose the whole wood. But there is evidence that 

 there were large "forests" in the interior of the islands, 

 consisting mainly of the iron-wood, Cordia siibcordata. 

 The largest island is said to be only about five miles long; 

 and the group is between 600 and 700 miles from the 

 nearest land, excluding the small Christmas Island. 



Already at the time of Darwin's visit in 1836, the 

 islands were in the possession of Captain Ross, the 



' " The Dispersal of Plants, as illustrated by the Flora of the Keeling or 

 Cocos Islands." A Paper read at a meeting of the Victoria Institute on 

 Monday, February 3, 1890, by Dr. H. B. Guppy. 



