June 2, 1881] 



NATURE 



lOI 



tube, and the date of filling. Something more exact than the 

 commercial name of the glass would be needed in stating the 

 former, but both of these particulars might with propriety be 

 engraved on the tube. Leonard Waldo 



Yale College, New Haven, May 1 1 



"How to Prevent Drowning" 



One further hint may be added to those of Mr. MacCormac. 

 It is as i-imple as practical, although it may not have been before 

 recommended in print. 



When a person is thrown into the water from an elevation the 

 body sinks for a time, and may not rise quickly to the surface to 

 permit fresh breath to be taken. In that case shut the lips firmly 

 to prevent the escape of the breath, and swallow the breath. 

 This is the art of the diver ; it conies naturally to him when he 

 seeks to prolong his stay under w ater ; but it may not as readily 

 occur to one unskilled in diving, whose only desire is to reach 

 the surface. The act of gulping down the breath may be 

 repeated three or four times, and thus protract the chances of 

 escajje. 



Although every one may tread water, fresh or salt, Mr. Hill 

 is undoubtedly right in saying that all cannot float upon fresh 

 water without assistance from their hands or feet. Not one in ten 

 can do so. When the swimmer shows his toes a>ove the surface 

 his hands are in constant action below, turning half-way round 

 from the wrist and back again, to change the fulcin.ent. 



Wm. Chappell 



Stratford Lodge, Oatlands Park, Weybridge Station 



The bathing — I might almost say the drowning — season is 

 now about to begin, and many lives will unhappily be lost. As 

 the human frame, bulk for bulk, is lighter than water, all that 

 is needful to save life is to permit the body to sink until it shall 

 displace as much water as equals the body's weight. Then 

 paddle gently, as the lower animals do, with hands and feet, the 

 head being held erect, wherever it is desired to go. This direc- 

 tion being carried out is absolutely all that is needful under 

 ordinary conditions to preserve life. These few directions 

 ought to be stuck up in every bathing-place — every boating- 

 and skating-place — in the three kingdoms. Children in 

 every instance ought to be made to tread water from the 

 earliest age, say in shallow slate baths with blood-viarm 

 wata', or, w hen convenient and suitable, in some river, pond, or 

 in the open sea. A leather belt with ring, and a stout rod with 

 line and hook, are employed by Portuguese mothers to instruct 

 their children. The mother, rod in hand, stands on the brink ; 

 the cliild learns in the water. In Paris swimming-schools the 

 same procedure is resorted to. The business cannot be begun 

 too soon. I saw mere infants sustaining them elves perfectly in 

 the tepid waters of Africa. Treading water is far safer than 

 Lwimming in a broken sea. Every adub, man or woman, who 

 has not practised it should begin. Once the convIctiDn instilled 

 that the body is lighter than water, the risk of drowning is 

 reduced to zero. The process involves no uncertainty, no delay. 

 Very different from swimming, it can be acquired at once. 



Belfast, May 25 Henry MacCormac 



Optical Phenomenon 



Mr. Murphy's experience, described in Nature, vol. xxiv. 

 p. 80, is general enough. It was observed by Fechner in i860, 

 and is now commonly associated with his name, though Prof. 

 Briicke of Vienna had also seen and explained the very same 

 phenomenon some years before that. Nor was he the first, for, 

 according to Aubert, there is a still earlier account due to Brewster 

 in Poggcndorff s Annalen for 1833. 



Fechner's side-window experiment, as it is called, is best seen 

 by eniploying a scrap of white paper on a black ground, or vice 

 versa, the eyes being accommodated for some other distance, so 

 that double images of the j aper are secured. Care must also be 

 taken tliat the light from the window enters the nearer eye only 

 through the sclerotic, so as to receive a reddish tinge. This dif- 

 fused reddish light renders the eye after a short time compara- 

 tively insensitive to red, so that the light reflected from the white 

 paper appears greenish, the black paper alone, from which no 

 light is reflected, appearing of the reddish tinge. In contrast 

 with this, in the other eye, which is sheltered by the nose from 

 the window-light, the white light appears reddish, and the black 

 greenish. Some little time is required for the illuminated eye 



to be exhausted for red before the contrast is very strikmgi 

 Such is Briicke's explanation; but who will ex plain to us this 

 "subjective phenomenon of contrast " ? James Ward 



Trinity College, Cambridge, May 29 



An Optical Illusion 



If your correspondent, Mr. William Wilson, will refer to 

 vol. xxxiii. of the " International Scientific Series," page 86, he 

 will find yiven by Prof. Le Conte a full description and expla- 

 nation of tlie ocular illusion to which he refers in his letter 

 (Nature, vol. xxiv. p. 53). The explanation is identical with 

 that given by yourself. SAMUEL Drew 



Chapeltown, Sheffield, May 24 



Occurrence of Neolithic Implements at Acton, W. 



It may interest your readers to know that I discovered, last 

 week, on the surface of a field south of the Priory at Acton, an 

 abundance of Neolithic implements, precisely similar as regards 

 form, type, -ize, and material to those which occur so abundantly 

 in the neighbourhood of Beer and Sidmouth, in Devonshire. 

 They occur also on a large field on the hill at Acton, wet of the 

 Wilesden Railway, and are formed of grey or black chalk flints, 

 which — or the implements — have been imported. On a field south 

 of the Priory I found a flat, circular, grey, quartzite, beach 

 pebble, derived possibly from the Bunter Conglomerate of South 

 Devon, similar to those of the Dorsetshire and Devonshire 

 coasts. Such pebbles are of frequent occurrence on the surface 

 of the fields in the Neohthic districts of Beer and Sidmouth, 

 and have been used as hammer stones and missiles. The asso- 

 ciation of this pebble with implements so like in every respect to 

 those of South-East Devonshire is very remarkable. 



The occurrence of palceolithic implements in the drift of Acton 

 has been known for some years. They occur in remarkable 

 abundance in the high level gravels of this locality as w ell as in 

 the low level gravels of Hammersmith, and one cannot fail to find 

 in newly -spread gravel examples of the minor implements, such 

 as flakes, drills, &c., and occasionally larger implements. A 

 series of the nenHthic implements of Acton 1 purpose depositing 

 in the jermyn Street Museum. Their discovery at this locality 

 confirrns the conjecture I had formed that neolithic implements 

 might occur in the Thames Valley, from having found imple- 

 ments of neolithic type in the drift, into which they may have 

 got washed. Spencer Geo. Perceval 



21, Netting Hill Square, W., May 20 



Birds Singing during Thunder 



A thunder-storm of great severity passed over us, travelling 

 round from west to south, between 4 and 8 o'clock p.m., May 

 28, and killing a man in the open air three miles from my resid- 

 ence. The thermometer stocd about 70" all the while. During 

 the storm, and even when the thunder-peals were loudest, the 

 chaflinches kept singing, and the blackbirds' notes alteniated 

 with the thunder-claps. The rain was moderate, and as the air 

 filled with insects and perfume, the swallows kept busily, 

 skimming even while forked lightning was flashing. Horses in 

 the fields' however exhibited symptoms of terror. J. Shaw 



Tynron, Dumfriesshire 



FireBalls 



I HAVE read with great interest Prof. Tait's lecture on 

 Thunderstorms, and have had recalled to mind a singular fire- 

 ball which I had the fortune to see some years ago during_ a 

 thunderst. rm in Portugal. I have a perfect recollection of the 

 phenomenon without referring to my journal of that dale. 



I was standmg in a window on the second floor of the Hotel 

 Braganza (in Lisbon), which stands clo-e to and hii;h above the 

 Tagus, and h.ad an imbroken view of the river. There occurred 

 a flash followed by an instantaneous crash, but the tail of the 

 flash, however, gave origin to two balls, which descended sepa- 

 rately and not far apart, towards the river, and when quite close 

 to, or in cjntact with the water, burst in rapid sequence, with 

 explo ions which might have been the crack of doom. 



Sumatra, April HENRY O. Forbes 



Sound-Producing Ants 



In Nature, vol xxii. p. 5S3, which has lately reached me, 



I read a letter fr^m Mr. Peal on sound-producing: auls, and I 



