102 



NATURE 



[May 30, 1889 



Meteorological Section of the Krakatab Committee of the 

 Royal Society — " that the highest air-current over the equatorial 

 doldrums is from the eastward, lying between the south-west 

 current which flows on one side over the north-east trade, and 

 the north-west current which flows on the other side over the 

 south-east trade." RALPH Abercromby. 



21 Chapel Street, London, May 27. 



The Structure and Distribution of Coral Reefs. 



I HAVE to thank Prof. Bonney for pointing out my error in 

 assigning the " 90-fathom reef" to Socotra instead of to Rod- 

 riguez. It arose from my having been accustomed to associate 

 Prof. Balfour's researches with the former island. 



With regard to the depths in which coral reefs can form, there 

 has been without a doubt some little concurrence of testimony 

 as far as the evidence goes. But I contend that all the observers 

 were misled by supposing that the sand and reef debris, that 

 nearly always prevent and repress the growth of corals in depths 

 of 20 to 30 fathoms, necessarily represented the lower limit of 

 reef-formation. We know little of the depths beyond this belt 

 of sand and reef debris, inasmuch as the observers in question 

 rarely extended their search beyond. The difficulties in 

 examining these depths are much greater, and systematic 

 soundings are greatly needed, being in fact only practicable in 

 the case of a surveying-vessel. 



Since writing my letter I have received, through the courtesy 

 of Captain Wharton, a copy of a report of the examination, in 

 1888, by Commander Moore and Dr. Bassett-Smilh, of H. M.S. 

 Rambler, of the slopes and zoological condition of the Tizard 

 and Macclesfield Banks. This report is, I believe, to be further 

 extended by Dr. Bassett-Smilh, so I will only quote here the 

 suggestive remark of Commander Moore, respecting the 

 Macclesfield Bank : "Coral was found living as far down the 

 slope as 44 fathoms ; it may extend further, but darkness put an 

 end to the work." I should also add that a living specimen of 

 an astraean coral was brought up from a depth of 45 fathoms in 

 the lagoon of Tizard Reef. 



Through the agency of the officers of Her Majesty's surveying- 

 ships, Captain Wharton will have soon at his disposal a large 

 amount of new material throwing considerable light on the origin 

 of coral reefs. H. B. GUPPY. 



Atmospheric Electricity. 



In Nature of May 16 (p. 55), Mr. Bowlker describes 

 some "curious" and, as he believes, "rare electrical pheno- 

 mena " which occurred to him and a friend oa the Welsh 

 mountains. Such phenomena are rare only because competent 

 observers are so. The effects described are by no means un- 

 common, and they may be classed under the brush discharge 

 and the glow, the one being an interrupted, and the other a 

 continuous, discharge to the air. 



H. de Saussure gives the results of his observations in 

 America, Switzerland, and other places. He remarks that the 

 lighting-up of the rocks at ni^ht is analogous to the curious fact 

 of electricity moving over the prairies. It is compared to a kind 

 of miniature lightning discharge, resulting from the electrified 

 cloud brushing over the earth, and discharging itself in thousands 

 of sparks coursing over the meadows. In Mexico he noticed 

 the crepitation of the stones due to electrical discharges, and in 

 Switzerland he describes certain pricking and burning sensations, 

 and sounds like that of simmering water, emitted from sticks laid 

 against the rocks, and from the tops of the alpenstocks. This 

 humming of the mountains is by no means rare, and it seems to 

 indicate a flow of electricity from the ground into the air. 



When Prof James Forbes was at work on the glaciers of 

 Switzerland, he noticed on one occasion, near Mont Cervin, a 

 curious sound proceeding from his alpenstock. The guide 

 referred it to a worm eating the wood ; he reversed the stick, 

 and the worm was already at the other end. He raised his 

 hand above his head, and the fingers yielded a fizzing sound, 

 while the angular stones all round were hissing like points near 

 an electrical machine. There was hail at the time, and a 

 thunderstorm soon set in. 



M. Trecul relates in the Comptes rendus the following curious 

 case : — While writing at an open window in August 1876, 

 between 7 and 8 a.m., he noticed a number of small luminous 

 columns descend obliquely on his paper, each about 2 metres 

 long, and half a decimetre broad at the widest part, obtuse at the 



farther end, but gradually thinning towards the table. They 

 had mostly a reddish-yellow tint, but near the paper the tints 

 were more intense and varied. In disappearing they left the 

 paper, with a slight noise, like that produced by pouring a little 

 water on a hot plate. Loud thunder was heard at the time of 

 the observation. 



In June 1880, at Clarens, near the Lake of Geneva, a cherry- 

 tree was struck by lightning, and a little girl who was about 

 thirty paces from the tree appeared to be wrapped in a sheet of 

 fire, while six persons, in three groups, none of them within 

 250 paces of the cherry-tree, were enveloped in a luminous 

 cloud. They said they felt as if they were being struck in the 

 face with hailstones or fine gravel, and when they touched each 

 other, sparks passed from their fingers' ends. At the same time 

 a luminous column was seen to descend in the direction of 

 Chatelard, and it is stated that the electricity could be distinctly 

 heard as it ran from point to point of the railing of the 

 cemetery. 



Mr. Jabez Brown, while ascending one of the sharp hills near 

 Bo-castle, in November, at 9 p.m., was suddenly surrounded by 

 a bright and powerful light, which passed him a little quicker 

 than the ordinary pace of a man's walking, leaving it as dark as 

 before. The light was seen by the sailors in the harbour, coming 

 in from the sea, and passing up the valley in a low cloud. A 

 similar one occurred in Scotland last year. 



Highgate, N. C. Tomlinson. ?| 



The electrical phenomenon described by Mr. Bowlker in 

 Nature of May 16 was doubtless an instance of St. El no's 

 Fire ; and if it had been dark at the time it was noticed, the post, 

 walking-stick, and other objects affected by it would have been 

 seen to be capped with a glow resembling somewhat the brtish- 

 discharge of an electrical machine. It has been observed about 

 fifteen times on the summit of Ben Nevis during the last five 

 years, and these cases are described, and the accompanying weather 

 discussed, in a paper by Mr. Rankin, of the Ben Nevis Obser- 

 vatory, published in the last number of the Journal of the 

 Scottish Meteorological Society. When it occurs, all elevated 

 points, whether metallic or not, glow ; the light in the more in- 

 tense cases being several inches in length. It is almost always 

 accompanied by a heavy fall of conical-shaped snow-flakes about 

 a quarter of an inch long, resembling hailstones in shape, but 

 not hard or icy. At all times when it has been seen the baro- 

 metric pressure has been high over the south or south-west of 

 Europe, and low to the north of Scotland, thus giving steep 

 gradients for westerly winds ; and in most cases the temperature 

 on Ben Nevis has been falling, while the barometer after falling 

 considerably has begun to rise again, and the wind to veer from 

 south-west towards north-west. ' R. T. O.MON'D. 



Ben Nevis Observatory, May 24. 



Sailing Flight of the Albatross, 



My attention has been drawn to some correspondence in 

 Nature, May 2 and 9, on the "Sailing Flight of the 

 Albatross," in which reference is made to my father's letter to 

 Sir William Thomson on the subject. At Sir William 

 Thomson's suggestion, I am now about to condense the rest of 

 my father's correspondence on the subject into a form convenient 

 for publication. In the meantime I will only say that while 

 Mr. Baines's very interesting letter, and his explanation of the 

 phenomenon of "soaring," appear to me perfectly sound in 

 principle (and indeed we have Lord Raylei;^h's authority for this 

 view), my father's statements seem to prove that his own solution 

 is also the true explanation of the soaring under the (different) 

 circumstances in which he observed it. It appears to me only 

 reasonable to suppose that the birds instinctively learn to avail 

 themselves of all the different natural conditions which under 

 different circumstances may serve them to maintain their flight 

 with the smallest exertion. R. E. Froude. 



Gosport, May 25. 



The Science and Art Examination in Physics. 



The paper set on May 17, in Sound, Light, and Heat, presents 

 several features that must have created dissatisfaction alike among 

 students and teachers. 



First, the official Syllabus explicitly states that the paper 

 " will be so arranged that a candidate can secure a first class in 



