28) 
NATURE 
[Way 4, 1871 

western coast, in the summer of 1868, the following incident 
came under my notice ; and, although I made a note of the 
facts at the time, I have never hitherto made them the subject 
of a scientific communication: On July 26, when approaching 
_ the strand at the river below the village of Newport, County 
Mayo, I noticed what appeared to be extensive streaks of scum 
floating on the surface of the water. As it was my intention to 
bathe, I was somewhat dissatisfied with the appearance of the 
water, until I stood on the edge of the strand, and I then per- 
ceived that what was apparently scum, seen from a distance, 
consisted of innumerable particles of sand, flat flakes of broken 
shells, and the other small @é%,7s which formed the surface of 
the gently-sloping shore of the river. The sand varied from the 
smallest size visible to the eye up to little pebbles, nearly as 
broad and a little thicker than a fourpenny piece. Hundreds of 
such little pebbles were afloat around me, and it is probable 
that the flakes of floating matter seen farther off contained also 
a considerable proportion. The air during the whole morning 
was perfectly calm, and the sky cloudless, so that, although it 
was only half-past nine, the sun had been shining brightly for 
some hours on the exposed beach. The upper surface of eazh 
of the little pebbles was perfectly dry, and the groups which 
they formed wereslightly depressed in curved hollows of the liquid. 
The tide was rapidly rising, and, owing to the narrowness of 
the channel at the point where I made my observations, the 
sheets of floating sand were swiftly drifting farther up the river 
into brackish and fresh water. On closely watching the rising 
tide at the edge of the strand, I noticed that the particles of sand, 
shells, and small flat pebbles, which had become perfectly dry 
and sensibly warm under the rays of the sun, were gently 
uplifted by the calm, steadily-rising water, and then floated 
as readily as chips or straws. I collected a few speci- 
mens of these little objects, but I regret that they have been 
since mislaid. This phenomenon, it is scarcely necessary to say, 
is due to molecular action, such as accompanies the familiar 
experiment of floating needles on the surface of a basin of water. 
Although the specific gravity of the floating objects exceeds that 
of the fluid on which they rest, the principle of Archimedes still 
holds good, because the displacement of liquid produced by the 
body is considerably greater than the volume of the body itself. 
In the case of a floating needle, the repulsion of the liquid from 
the polished surface of the metal presents a groove, whose mag- 
nitude is obviously many times greater than the needle; but 
in the case of the floating pebbles this was not so manifest. 
The attraction of the molecules of water for one another 
produces, as is well established, a tension at the surface 
of the liquid, which, although extremely feeble, and generally 
noticed only in connection with capillary phenomena, yet in- 
terposes some resistance to the intrusion of foreign substances. 
I have floated small flat pebbles, similar in size and ap- 
pearance to the largest of those observed floating on Newport 
river, for more than six days, while fragments of shells, 
and thin pieces of slate as broad as a sixpenny-piece, have 
continued to float much longer. These little bodies occasionally 
sank from the gradual absorption of water, but much more 
frequently from some accidental motion of the vessel con- 
taining the liquid. It is manifest that the floatation of sand ina 
tidal estuary, as in the instance I have seen, can occur only under 
favourable conditions. The shores must be very gently inclined, 
the air perfectly calm, and the weather dry and warm. Under 
these circumstances thin cakes or sheets of sand may not only be 
uplifted by the water, but if the tide flows rapidly they may con- 
tinue to float sufficiently long to allow many of them to be drifted 
far from their original place up to the higher limit of the brackish 
water. In this way fragments of marine shells and exuvize might 
become mingled with those belonging to fresh water. The con- 
ditions favcurable for sand floatation must exist during calm 
weather in a very high degree of perfection on the sandy shores 
of tidal rivers in tropical and subtropical districts of the earth. 
As this phenomenon can take place only with the rising tide, and 
never with the falling tide, the result must generally be favour- 
able to the transport of sand and marine débris in the direction 
of the flow of flood tide ; and this may sometimes hold good 
along a coast as well as on the shores of a tidal estuary. Geolo- 
gists, as far as I am aware, have not hitherto noticed this phe- 
nomenon in connection with the formation of stratified deposits 
by the agency of tides and rivers, although they have paid great 
attention to the influence of the molecular resistance of water to 
the sinking of very minute solid substances, with the view of ex- 
plaining the wide surface over which matter held in suspension 
hy wa'er may be spread when ultimately deposited oyer the sea 


bottom.—Prof. W. King read a paper, by himself and Prof. 
Rowney, “On the Mineral Origin of the so-called Zoz00 Cana- 
dense.” Tt was resolved to purchase the Bell and Bell-Shrine of 
St. Patrick, from Dr. C. Todd, for the sum of 500/. 

BOOKS RECEIVED 
ENGLIsH.—Travels in the Air: J. Glaisher, 2nd edition (R. Bentley).— 
The Natural History of Plants: H. Baillon, vol. x, translated by N. Hartog 
(L. Reeve and Co.).—Primitive Culture, 2 vols.: E. B. Tylor (J. Murray). 
—On Aphaxia, or Loss of Speech: Dr. F. Bateman (Churchill), i 
Foreicn.— (Through Williams and Norgate)— Archiv fiir Anthropologie, 
vol. iv.—Zeitschrift der oesterreichischen Gesellschaft fiir Meteorologie, vol. 
y.—Compendium der chirurgischen Pathologie u. Therapie: Dr. C. Heitz- 
mann. 



DIARY 
THURSDAY, May 4. 
Royat Soctety, at 8.30.—On the Structure and Affinities of the Gwynia 
Annulata (Dunc.), with Remarks upon the Persistence of Palzozoic Types 
of Madreporaria: Prof. Duncan, F.R.S.-_On Molybdates and Vanadates 
ot Lead, and on a new Mineral from Leadhills: Dr. A. Schrauf. 
Society OF ANTIQUALIES, at 8.30.—Roman Villa at Beddington: J. Addy. 
—Antiquities from Cyprus: J. B. Sandwith. 5 te : 
LinnEAN Socrety, at 8 —The phenomena of Protective Mimicry, and its 
bearing on the Theory of Natural Selection as illustrated by the Lepidop- 
tera of the British Islands: Raphael Meldola, F.C.S.—On the Ascala- 
phide : R. McLachlan. nie. ; 
CHEMICAL Society, at 8.—On the Productive Powers of Soils in relation to 
the Loss of Plant Food by Drainage : Dr. Voelcker, F.R.S. 
Roya InsTITuTION, at 3.—On Sound: Prof. Tyndall. 
Lonpon INSTITUTION, at 7.30.—On Economic Botany: Prof. Bentley. 
FRIDAY, May 5. 
Gerotoaists’ AssoctaTION, at 8.—On the Fauna of the Carboniferous Epoch: 
H. Woodward, F.G.S. 4 
Royat InstiTuTION, at 9.—On Russian Folk-Lore : W, R. S. Ralston. 
SATURDAY, May 6. 
Roya. Scuoor or Mints, at 8.—Geology : Dr. Cobbold. 
Roya Institution, at 3.—On the Instruments Used in Modern Astro- 
nomy: J. N. Lockyer, F.R.S. 
MONDAY, May 8. 
Roya GEOGRAPHICAL SOCIETY, at 8.30. 
Roya INSTITUTION, at 2.—General Monthly Meeting, 
Lonpon Institution, at 4.—On Astronomy: R. A. Proctor, F,R A §, 
(Educational Course.) 
TUESDAY, May 9. 
PHOTOGRAPHIC SOCIETY, at 8. 
Royat InstirTution, at 3.—On Force and Energy: Charles Brooke, F.R.S. 
WEDNESDAY, May 10. 
Society or Arts, at 8.—On the Application of Steam to Canals: Geo. Ed- 
ward Harding, C.E. 
Geotoaicat Society, at 8.—On the Ancient Rocks of the St. David's Pro- © 
montory, South Wales, and their Fossil Contents: Prof. R, Harkness, 
F.R.S., and Henry Hicks.— On the Age of the Nubian Sandstone: Ralph 
Tate, F.G.S.—On the Discovery of the Glutton (Guéo Zuscus) in Britain? 
W. Boyd Dawkins, F.R.S. 
THURSDAY, May 11. 
Roya Society, at 8.30. 
Society oF ANTIQUARIES, at 8.30. 
MATHEMATICAL Soctery, at 8.—On the Singularities of the Envelope of a 
nou-Unicursal Series of Curves: Prof. Henrici. 
Royat Institurton, at 3—On Sound: Prof. Tyndall. 


CONTENTS 
Pace 
Tue SMALLER LecTURESHU’s AT THE LonDON Mepicat Scuoots, I, 
Tue CONSERVATION OF FoRCE . tee I 
Tue LiveRATURE OF CHEMISTRY. . ats oMteh us| bie 5 2 
GratsuERr’s TRAVELS IN THE AIR. (With Iitustrations.) ge tee 
Our Book SHELF . oegomheg elpieltic: fer ke 4 
LETTERS TO THE EpiToR:— 
Pangenesis.—F. Gatton, F.R.S. . es 
The Hylobates Ape and Mankind ey Oe) 6 reer 
Tables of Prime Numbers —J. W. L. GLAISHER . . - 6 
Units of Force and Energy.—Prof. J.D. Everett. . 6 
Mh! Namie S56 rita.) onus etc cose ae Site 7 
Derivation of the Word ‘‘ Britannia.” —Hype CLARKE . 7 
Aurora by Daylight.—J. JEREMIAH Lead 7 
The Irish Fern in Cornwall —W. P. Dymonp . 8 
Prevalence of West Winds.—J. K. Laucuton 8 
SuBMARINE TELEGRAPHS. By N. J. Hommes . ares 
PriuGer’s Nerve EnpincsinGLanps .... . « + 10 
NOTES Ko fie ice ie Fouls: A &) spe jhe vet ich) CR ee 
Tue Royat Soctery’s List For 1871 = Boe ete a tee > Siow) eer 
On Corour Vision. By Prof. J. Clerk Maxwe t, F.R.S. 3 See 
ScrenTiFIc SERIALS . . . ou)! Chen. eo oe ch ail : 16 
Socisties anp ACADEMIES. . . . ° . 5 oe ey 
Books RECEIVED < < 20 
TARY Sak cu te eer (octet ac eon 
