November, 1901.] 



KNOWLEDGE. 



:i.l 



T^IUUSTRATEp MAGAZINE <i 



^^^CEJLiTERAiyREJt ART/ 



Founded by RICHARD A. PROCTOR. 



Vol. XXIV.] LONDOy : XOVKMBER, 1901. [No. 103. 



CONTENTS. 



The Sinking of Large Stones through the Action of 

 Worms. Hy Chahf.ks Pa\ ison, sc n., i.c.s. (Ilhislraleil) 



The White Nile — From Khartoum to Kawa. V. 

 Birds. Hv Harry Y. Witiierbt, i'./..s., M.u.n.r. 

 (lUvxtrated) 



The Insects of the Sea. — VI. Four-Winged Flies and 

 Bugs. By Geo. U.CARrENTKR, B.3C.(i,0Ni).) {Illiistra(eil) 



Constellation Studies.— X. The Royal Family. ?,\ 

 E. WaITFR llArXDBR, F.R.A.S. (lUu.itrateilJ 



Nova Persei. By K. M. Axto.vi.miI, f.r.a..~. {Illustrated) 

 Photographic Images of Nova (3,1901) Persei. {Plate.) 

 Letters : 



Beiiliant Meibob i>' California. By S. D. Proctor 



Does the Moox Affect Raixfall? By Alf,x. B. 



MacDowall. (IlhistratedJ 



Some Peculiar Animal Products. By R. Ltdekker . 

 British Ornithological Notes. Conducted by Harrt F. 



WlTHERBT, F.Z.S., JT.B.O.r. ... 



Notices of Books 



Books Eeceited 



Notes 



The Alchemy of Hoar-Frost. By Abthub II. Bell. 



The Water of the Dead Sea. By C. Aixswoeth 

 Mitchell, b.a., f.i c. 



Microscopy. Conducted by if. I. Cross 



Notes on Comets and Meteors. By W. F. Dennino, 

 r.s.A.s. ' ... 



The Face of the Sky for November. By A. Fowleb, 



f.b.a.s ' 



Chess Column. By C. D. LococK, b.a. 



2U 



243 



-' t."> 



2t.S 

 2.")0 



251 



251 

 251 



251 



254 

 25i: 

 25r, 

 25S 



250 



2{;() 



262 



262 

 2C3 



THE SINKING OF LARGE STONES THROUGH 

 THE ACTION OF WORMS. 



By Charles Davison, sc.d., f.g.s. 



Twenty years have passed since Mr. Darwin puljlislicl 

 his last work.* If in his '' Descant of Man," as one 

 reviewer reniaikod. he ha<l put down tlie mighty from 

 their seat, in his " Vegetable Mould ' he exalted them 

 that arc of low degi-ee, and few of his many oliservafions 

 are more interesting than those which relate to (he 

 habits and rude intelligence of earth-worms. Ec|ually 

 valuable and no less surprising were his mca,suremeii(s 

 of the amount of soil brought to the surface by worms 

 and of the i-ate at which layers of stones were covered 

 by their castings. In different places, the castings were 



* " The Formation of Vegetable Mould, etc." (Murray, 1881.) 



collected regularly over measured areas and were found 

 to yield a layer of .soil which, if spread over the same 

 area*, would in ten years vary from about one. to onc- 

 and-a-haU" inches in thickness. The depth of mould 

 which accumulated over small stones strewn on the 

 surface of fields was found, after intervals of seven to 

 nearly thirty years, to range I'lom 1.9 to 2.2 inches in 

 ten years. 



" When a stone of large size and of irregular shape,' 

 says Mr. Darwin, " is left on the surface of the ground, 

 it rests, of course, on the more protuberant parts ; but 

 worms soon fill up with their castings all the hollow 

 spaces on the lower side ; for, as Henscn remarks, they 

 like the shelter of stones. As soon as the hollows are 

 lilled lip, tlio worms eject the earth which they have 

 swallowed bevond the circumference of the stones ; and 

 thus the surface of the ground is raised all round the 

 stone. As (lie burrows e-xcavatcd directly beneath the 

 stone after a time coUap.se, the stone sinks a little. 

 If, luiwcver, .-i boulder is of such huge dimen- 

 sions, tliali (he c>;irlli beneath is kept dry. such earth 

 will not be inhabited by worms, and the boulder will 

 not sink into the ground." 



Mr. Darwin gives several examples of this gradual 

 sinking of large, stones. It will be sufficient for our 

 present purpose to ciiioto one. A block of ciuartzose 

 sandstone, C4 inches long, ]7 inches broad, and from 

 9 to 10 inches in thickness, had been left on a bare 

 surface of broken bricks and mortar. Thirty-five years 

 later, when it wa.s examined by Mr. Dai-win, the ground 

 surrounding the stone was covered with turf and mould, 

 which for a distance of about nine inches round the 

 stone gradually sloped up to it, and close to it the sur- 

 face was about four inches above the surrounding 

 ground. The lower surface of the stone was uneven, 

 and the projections were still found resting on the brick- 

 luhbish, but the intervening spaces were filled up by 

 worm-castings, so that, when the stone was removed, an 

 exact cast of its lower side was left. The whole stone 

 had sunk about 11 inches in the 3.5 years, that is, at 

 the rate of .■l.'i inch in ten years. 



This estimate, however, must be less than the tine 

 amount, for some time would bo lost in filling up the 

 vacant space below the stone; and, in order to determine 

 the rate more accurately, an experiment was commenced 

 in the autumn of 1877 by Mr. Darwin's youngest son 

 and continued during an interval of nearly twenty years. 

 The results of this work were communicated to the 

 Royal Society last May in a short paper, of which the 

 present is an abstract.! 



The place selected for the purpose was a nearly level 

 field near Mr. Darwin's house at Down, which had 

 probably been pasture for more than fifty years, and 

 under a large Spanish chestnut tree. J A circular stone 

 about 18 inches in diameter and 2] inches thick, and 

 weighing about 41 lbs. was laid upon the ground. A 

 hole was m.ade through its centre and was lined with a 

 brass cylinder, containing on the top three horizontal 

 projecting pieces leaded into the upper surface of the 

 stone. In each of these pieces, a radial V-shaped groove 

 was cut. 



t Horace Darwin : " On the .small vertical movements of a .itone 

 laid on the surfai-o of the {ground. " Hoy. Noc. Proc, Vol. LXVKI., 

 J901, pp. 253-26J. A preliminary iieeount of the experiment was 

 given by Messrs. Cr. If. iin<l If. Diirwin, in their report on (he lunar 

 disturbance of gravity. Bril. Assoc. Hep , 1881, ])p. 123, 123. 



t This situation was afterwards seen to lie unf'avonrable. Move- 

 ments of the stone might be <'aused by the growth of the roots, and 

 worm-castings are sometimes absent underneath trees. 



