April 29, 1920] 



NATURE 



> signifying a stream. Leland the Chronicler wrote 

 :hat "there runneth a praty lake out of Sudeley 

 Parke down by the Castle and runneth into Esse- 

 bourne Brook at the south syde of Winchcombe." 

 And again : " I passed over 2. or 3. small lakes 

 betwixt Chiltinham and Gloucester and they resort 

 to Severne. " The word is still used in some places 



-^ meaning a stream; children on the Severn banks 



ill sing of the moon as claiming to guide the ship 



up the lake." 



The first Lord Avebury, in writing of meanders 



Scenery of England "), mentions, as one of the results, 

 ' that the loop often remains as a dead river-channel or 

 mortlake. " Such loop-lakes are known in America as 

 "oxbows." There is, however, a great difference. In 

 the case of an "oxbow " the loop, formed by a lateral 

 deviation of the river, has been entirely cut off from 

 the main stream. A mortlake may be defined as the 

 line of a closed part of one of the two sections of a 

 river (previously divided so as to surround an island 

 in the stream), the other channel remaining open and 

 serving as a single channel for the river. 



Of the two sections of a river enclosing an island, 

 one of them at least must have a curved line. Two 

 straight lines cannot enclose a space. If, then, the 

 whole or a part of the stream in one of the sections 

 be etfaced, the remaining section, now forming the 

 whole of the river, must have a more or less curved 

 line. It must be a river-winding. The form and the 

 length of it will, of course, depend on the shape and 

 on the size of the former island. Thus a result of 

 the formation of a mortlake may be one of those 

 meanders or river-windings which are a familiar and 

 picturesque feature in the landscape. The explanation 

 of them has been a puzzle from classic times until 

 the present. The subject was discussed at length by 

 six contributors to Nature in November and December, 

 1907. 



I have come to the conclusion that the conversion 

 of river-islands into areas bounded by single streams, 

 more or less curved, is part of the ordinary course of 

 river development. This, in my view, may be briefly 

 stated thus : A newly exposed part of the earth's sui- 

 .face receives the rainfall on every square inch of it, 

 but the water will not flow away in the form of a 

 sheet; minute runnels form, and these will not be in 

 straight lines parallel to each other. I cannot imagine 

 straight "primary consequent streams" as they are 

 sometimes depicted. Even slight obstructions would 

 turn them aside so that they would meet and coalesce, 

 thus forming a miniature network of streams, each of 

 the meshes enclosing an islet. Then the water on the 

 up-stream side of every islet will have alternative 

 routes before it. These routes may, for a time, be 

 equally easy, but they will not continue to be so; 

 one of them will be preferred, and this may not be 

 the most direct. The stream which continues may 

 Ije the one which meets with the least obstruction, or 

 it may be the one most necessary for continuance as 

 having to receive longer or more numerous tributaries. 

 A channel no longer needed will cease to be used; it 

 will silt up. Then the islet will become continuous 

 with an adjoining islet. This process being many 

 times repeated, islands of increasing size — which may 

 be large and, possibly, of very great extent — will result. 

 Ultimately, they will all cease to be islands, in the 

 absence of need for two channels. The development, 

 in my view, is not /rom "primary streams" m\o a 

 " coniplicated network" of channels, but from the 

 complexity of a network of channels towards the sim- 

 pliritv of one principal strearn with tributaries cofi- 

 verging towards it. Certain it t$ thajt ip a river 

 systjpm as we see it there i?. np network. 



I. do, p/ot. vvis^..to augf^st.^hat the formation, of j 

 mortlakes is the only cause of river winalngs. Thirty-' 



NO. 2635, VOL. 105] 



seven years ago I pointed out (in a paper read before 

 a local society, and printed at the time) the influence of 

 tributaries as one cause ; and I recognise others. But 

 the same laws govern the development of all rivers. 

 Although Herodotus found the rivers of Egypt to be 

 different from other rivers, I, in imagination, see the 

 life-history of the Nile as very strikingly depicted in 

 its present course. I have elsewhere shown ("The 

 I Lower Severn," Proceedings of the Cotteswold 

 ; Naturalists' Field Club, xvi., 1909) an outline picture 

 of a thousand miles of the Nile below Khartum com- 

 ! pared with one of ten miles of the Severn below 

 j Gloucester. The resemblance is so close as to lead 

 [ to the remark that it almost seemed as if the one 

 I figure had been drawn in ink on the second page of a 

 j sheet of paper and the other by pressing the ink 

 1 before it was dry against the opposite page. The 

 I size of the two rivers and the character of the rock 

 formations being so very different, it is at least 

 remarkable that the course of the two should be so 

 very much alike. In the Times of a recent date 

 (March 15) is a report from Dr. Chalmers Mitchell 

 of his view from an aeroplane in passing above the 

 railway between Wady Haifa and Abu Hamed. He 

 saw " huge cliff-lines submerged at intervals by 

 desert," which suggested the "proper bed" of the 

 Nile. It is really a relic of the time when the area, 

 now partly enclosed by the great sickle-shaped curve 

 of the Nile, was a huge river-island two hundred miles 

 wide and five hundred miles long. That which Dr. 

 Chalmers Mitchell saw was the line of the easterti 

 arm of the Nile; it is now the line of a long mort- 

 lake. T. S. Ellis. 

 59 Park Road, Gloucester. 



Eiffel Tower Wireless TIme-Signals. 



It may interest a number of readers of Nature to 

 know that the Eiffel Tower is at present sending out 

 two additional sets of "scientific" time-signals. The 

 scientific signals are arranged as a time-vernier, 

 gaining about one beat in fifty. They have hitherto 

 been sent at 11.30 p.m. G.M.T., followed at 11,^5, 

 after the ordinary time-signal is concluded, by 

 numbers which give the moment of the first and the 

 last signal of the set, according to the standard clock 

 of the Observatory of Paris. A comparison can thus 

 be made with the introduction of a very small error, 

 often not exceeding one-fiftieth of a second. These 

 valuable signals have suffered from two awkward 

 features : In summer time they are inconveniently 

 late, and the purring or snoring note {ronfl^e) on 

 which they are sent is much obscured by atmospherits 

 when the latter are bad, so that sometimes one failed 

 to pick up the identification breaks which occur at the 

 end of every sixty beats. 



In addition to the old series, which remain un- 

 changed, two new series are now being sent ; these 

 are on wave-length 2600 metres and a hiijh 

 musical note that cannot be confused with atmo- 

 spherics. Otherwise they are the same as the orifjirial 

 — 300 dots, the 60th, i2oth, 180th, and 240th bemg 

 suppressed. They are sent: (i) at 10.30 a.m. 

 G.M.T., the comparison numbers giving Paris ^ime 

 following after completion of the 16.45' OT^inary 

 signal; and (2) at n p.m. G.M.T., the' >bjp- 

 parison numbers being sent after the 11.45 ordii^ary 

 signal, along with those which refer to the old fX-\o 

 signal, the two ref^reijces being distinguished bv t^e 

 letters ML imustcale) cind RF (roh/?^e) resppctV^Jy. 

 The new series are beaiitifujly cl^ar, and' 6ught to be 

 of great service to those who require accurnte time. 



. R. A. SAMfScai' 



Ri3yarObs«-vatory,"^diHBii^gh;' Ajirit^^^^^^ "^ 



