26o 



NATURE 



{July 2 1, 1 88 1 



beyond controversy, for your geoid makes no pretensions 

 except to irregularity. 



The surface of the geoid is in fact at every point per- 

 pendicular to the direction of gravity there. Thus the 

 surface of the (unagitatedj sea is a geoid, the surface of 

 all lakes are portions of geoidal surfaces, nearly but not 

 exactly parallel to that of the sea. That particular 

 geoidal surface which represents the figure of the earth 

 is the sea surface, which indeed is an old enough idea 

 with a new name. 



The work may be characteri.-ed as a fairly successful 

 attempt to combine the advantages of a scientific and a 

 popular treatment of its subject. It does not claim 

 originality, and the mechanical theory of the earth's figure 

 is not touched on. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 



[ The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible othenvise to ensure the appearance even 

 of communications containing interesting and ncrel facts.] 



Special Solar Heat- Radiations and their Earth-felt 

 Effects 



I REGRET if, by the words "lagging behind " in my paper to 

 Nature, vol. xxiv. p. 150, I have inadvertently misrepresented 

 the views of Prof. I'iazri Smyth. Had his paper been only 

 recently published, I might have been able to i-lead ignorance of 

 its contents, but it iv one which was published in 1869, and 

 which I have read several times in the belief that it contains not 

 only the first, but lil>ewise the most C'^mplete contribution to this 

 branch of knowledge. 



Having made this confession, let me now in a very words 

 endeavour to render clear that which I intended to say. 



The hypothesis advocated i 1 the lectures to which Prof. Smyth 

 alludes was that which represents the sun as most powerful rthen 

 it has most spots on ils surface Nevertheless if we take the 

 observations of Prof. Smyth, of Mr. Stone, and of Dr. Koppen, 

 and bring them together, we are led to think that perhaps on the 

 whole we have highest temperatures about those times when 

 there are fewest spots on the sun's surface. I then endeavoured 

 to show that such an experience was nevertheless not inconsistent 

 with the hypothesis of increased soUr heat daring times of most 

 sun-spots. 



Again, if we take rainfall, while we find that perhaps on the 

 whole there is most rain during times of maximum sun-spots, 

 yet there are certain stations which form an exception to this 

 rule. Nor is this to be wondered at if we reflect that the direc- 

 tion, as well as the intensity, of the earth's convection currents 

 must be affected by solar variability, and bear in mind that local 

 causes have a very powerful influence upon rainfall. Noh this 

 last remark applies to temperature as well. I should therefore 

 be prepared to hold, simply as a working hypothesis — 



1. That, on the v\h ile, the temperature on land may be less at 

 times of maximuTi than at times of minimum sun spots. 



2. That, on the whole, the rainfall on land may be greater at 

 times of maximum than at times of minimum sun-spots. 



3. That while a period of temperature and one of rainfall 

 coinciding with the sun-spot period will probably be fouul at 

 most stations, nevertheless in individual localities the turning- 

 points of these periods may vary considerably from the rule laid 

 down in I and 2. 



4. That the above order of phenomena is not inconsistent 

 with the hypothesis that the sun is most powerful when there 

 are most spots on its surface. 



In conclusion permit me cordially t'l assent to the remarks of 

 Prof. Smyth about the possibility of rapid outbreaks of solar 

 heat being responded to by the earth ; it may be only a few 

 hours afterwards. His Madeira observations are of great 

 interest to those who, like ourselves, believe that the bond 

 between the sun and the earth is more intimate and sympathetic 



and less formal in it. nature than that which the older genera- 

 tions of astronomers have been accustomed to imagine. 



14, Queen's Road, Bayswater Balfour Stewart 



How to Prevent Drowning 

 I OBSERVE several letters in Nature, vol. xxiv, pp. loi and 

 126, on floating as a means of preventing drowning, but I do 

 not think the last word is yet said on this subject. I fully agree 

 with Dr. Dudgeon that no rules for preventing drowning are of 

 any practical value, and also with Mr. Hill and Dr. Dudgeon 

 that those who can float are the rare exceptions. According to 

 my observation not one in ten, in fact I might say hardly one in 

 100 even, of good swimmers can float in fresh water in any 

 useful fashion, i.e., lying motionless on the water and breathino' 

 easily. The obvious reason is that the human bDdy in the 

 natural condition, i.e., with the lungs half itiflated, is specifically 

 heavier than water. Many persons say they c.in float, hut in 

 most cases they either inflate the lungs and h ild the breath, or 

 else they make slight movements of the hands. 



But Dr. Dudgeon is wrong in supposing that the exceptions 

 are all fat men. I am myself a case in point. I am slender 

 almost to meagreness, and yet I float easily. From boyhood I 

 have been fond of all athle'ic sports, and es.^ecially I am a prac- 

 tised and expert swimmer. I swim almost as easily as I walk. I 

 float even in fresh water with the utmost ease, and for any length 

 of tioie, breathing niCanwhile naturally. While floating, the 

 whole face, a large area on the chest, a small spot on the 

 knees, and the tips of the toes are above the surf.-ice. Breathing 

 causes the body to rise and fall gentlj', so that the exposed areas 

 of the face and chest increase and diminish alternately. 



It is evident therefore that the cases of persons who can 

 really float ai-e of two kinds, viz., (i) Those who are very fat, 

 and (2) slender persons with very small bones and proportion- 

 ately large lungs. This latter is my case. I never knew a 

 heavy, muscular, large-boned man withouf excess of fat who 

 could float. .Such men make powerful swimmers, but are less 

 easy and graceful in the water than those who are slenderer. 



Berkeley, California, June 27 Joseph Le Conte 



Optical Phenomenon 



I INCLOSE copies of photographs from two negatives (as you 

 may see by looking at the points stereoscopically) of the Cyclopean 

 gallery at Tiryns, for the sake of calling attention to the optical 

 phenomenon shown in it. The gallery is very dark, the only 

 hght entering it by the narrow entrance and crevices between 

 the rocks. At the extreme end of the gallery is an opening to 

 the sky large enough to put one's hand through. In the photo- 

 graph this is shown as a nucleus by a black speck surrounded by 

 bright light, around which appears a dark circle, which again is 

 encircled by a halo as perfectly rendered as one can see that 

 around the moon at times. The dark nucleus is larger in the 

 negative which had the longest exposure (the irregular lights 

 around are only the light falling on the stones from side openings 

 not visible). There was no such phenomenon recognisable to 

 the naked eye. 



The exposures were 25 and 15 min. with the full opening of 

 the Ross " portable " lens and a gelatine plate. 



Athens, July 3 W. J. Stillman 



[The photographs quite bear out Mr. Stillman's statements. 

 —Ed.] 



Implements at Acton 



In reply to the letter of Mr. Worthington G. Smith (Nature, 

 vol. xxiv. p. 141), the Pala;olithic implements at Acton I found 

 in a gravel pit on the hill we t of the North London Railway, 

 and from spread gravel which was local. Those I obtained at 

 Hammersmith occurred in gravel raised on a piece of ground 

 (Mr. Butt's) south of Great Church Lane, where building is 

 going on. They consisted of a hollow scraper, drill, &c., which 

 I readily found ; but the implements here seem ruder than at 

 Acton, and less easy of detection. I also found implements in 

 gravel raised from the foundations of the neighbouring houses, 

 which had been spread on some newly-made roads south of 

 Shepherd's Bush, between the Uxbridge Road and Addison 

 Road Stations. I see no reason for supposing that the imple- 

 ments here or at Hammersmith occur under different conditions 

 from those at Acton. 



