I^O 



NATURE 



[Dec. 1 6, 1875 



i2i> G.M.T. 



1729, July 31 ... 

 „ Aug. 8 ... 



1730, Jan, 18 ... 

 „ „ 31 •• 



Distance from 



Sun. 

 .. 4-065 .. 

 .. 4-072 .. 



• • 4'452 .. 



• • 4'499 ■• 



Distance from 



Earth. 

 ... 3-121 

 ••• 3T34 



•■• 5-152 

 ... 5-225 



For comparison with these distances take the case of the 

 great comet of 1861, which was observed by Mr. Otto 

 Struve at Poulkova till 1862, May i, when its distance 

 from the sun was 4*46, and from the earth 470 ; or that 

 ofMauvais's comet of 1847, followed by Bond with the 

 great refractor at Cambridge, U.S., till 1848, April 21, 

 and then distant from the sun 3-85, and from the earth 

 4*40 ; or again, the case of the celebrated comet of 181 1, 

 last seen by Wisniewsky at Novo-Tcherkask, 1812, 

 August 17, when the radius-vector was 4*54, and the 

 distance from the earth 3-50. 



RUTI MEYER ON TRACES OF MAN RE- 

 CENTLY DISCOVERED IN THE INTER- 

 GLACIAL COAL-BEDS OF SWITZERLAND 



THE last number of the ArcJiiv fiir Anthropologie 

 contains a short but important article by the emi- 

 nent zoologist of Basle, Prof. Riitimeyer, on some traces 

 of man recently discovered in the interglacial coal-bed at 

 Wetzikon. Escher von der Linth first called attention to 

 the fact that at several places in East Switzerland, espe- 

 cially on the eastern shore of Lake Zurich from Wetzikon 

 to Utznach, and again in the neighbourhood of the Lake 

 of Constance, there are beds of coal, which are not only 

 covered by, but which also repose on, well-marked glacial 

 deposits, thus clearly proving the existence of more than 

 one period of extreme cold, as first remarked by Morlot, 

 and since confirmed by many observers, and especially 

 by Geikie. 



These interglacial coal-beds contain numerous remains 

 of plants and animals, among the most interesting being 

 those of Elephas antiqujis and Rhinoceros tnerkii. The 

 remains of plants are indeed so numerous that Dr. 

 Scheuermann, of Basle, has been in the habit of breaking 

 up himself all the coal used as fuel in his house, in search 

 of vegetable remains. In doing so he was struck on one 

 occasion by observing a number of pointed rods lying 

 side by side, and he placed the block of coal containing 

 them in the hands of Prof. Riitimeyer. 



Prof. Riitimeyer has now given a description and 

 figures of these rods, from which it is clear that they 

 have been intentionally pointed, and that they formed a 

 portion of rough basket or wattle work. They are four 

 in number, and are closely embedded in the coal, which 

 they precisely resemble in colour, while the texture is that 

 of the ordinary wood found in these coal-beds. More- 

 over, as is usual in such cases, the stem has been com- 

 pressed, so that the section is not circular but oval. Ac- 

 cording to Prof. Schwendener, the wood is that of Abies 

 excelsa. The points bear evident traces of cutting, while at 

 one part of the rods are marks as if of a string wound round 

 and round them. Here, then, we appear to have clear 

 evidence of the existence of man during one of the warm 

 intervals of the glacial epoch. J, L. 



THE THEORY OF "STREAM LINES " IN RELA- 

 TION TO THE RESISTANCE OF SHIPS * 

 III. 



In this treatment of the propositions concerning the flow of 

 fluid through pipes, I have at length laid the necessary founda- 

 tion for the treatment of the case of the flow of an infinite ocean 

 past a submerged body. I have shown these propositions to be 

 based on principles which are undeniable, and the conclusions 



* Address to the Mechanical Section of the British Association, Bristol, 

 August 25, 1875 ; by William Froude, C.E , M.A., F.R.S. President of 

 the Section. Revised and extended by the author. Continued from p. 93. 



from which, when in any way startling or paradoxical, you have 

 seen confirmed by actual experiment. 



I have dealt with the case of a single stream of uniform sectional 

 area (and theri fore of uniform velocity of flo>v) enclosed in a 

 pipe of any path whatever ; I have dealt with the case of a single 

 stream of very gradually varying sectional area and velocity of 

 flow ; and I have dealt with the case of a combination (or faggot, 

 as it were) of such streams, each to some extent curved and to 

 some extent varying in sectional area, together composing the 

 whole content of a pipe or passage having enlargements or 

 contractions in its course ; and in all these cases I have shown 

 that, provided the streams or pipe-contents finally return to their 

 original path and their original velocity of flow, they administer 

 no total endways force to the pipe or channel which causes 

 their deviations. 



I am now going to deal with a similar combination of such 

 streams, which, when taken together, similarly constitute an in- 

 finitely extended ocean, flowing steadily past a stationary sub- 

 merged body ; and here also I shall show that the combination 

 of curved streams surrounding the body, which together consti- 

 tute the ocean flowing past it, r eturn finally to their original 

 direction and velocity, and cannot administer to the body any 

 endways force. 



The argument in this case is, in reality, precisely the same as 

 that in the case of the contractions and enlargements in pipes 

 which I have already dealt with ; for, in fact, the flow of the 

 ocean past the stationary submerged body is only a more 

 general case of the flow of fluid through a contracted pipe ; but, 

 though the cases are really the same, there is considerable differ- 

 ence in their appearance ; and therefore I will proceed to point 

 out how the arguments I have already used apply equally to 

 this case. 



Every particle of the fluid composing the ocean that passes the 

 body must undoubtedly follow some path or other, though we 

 may not be able to find out what path ; and every particle so 

 passing is preceded and followed by a continuous stream of 

 particles alL following the same path, whatever that may be. 

 We may, then, in imagination, divide the ocean into streams of 

 any size and of any cross-section we please, provided they fit 

 into one another, so as to occupy the whole space, and provided 

 the boundaries which separate the streams exactly follow the 

 natural courses of the particles. 



I before suggested a similar conception of the constitution of 

 the ocean flowing past the stationary body, and there pointed 

 out that the streams forming this system must not only be curved 

 in order to get out of the way of the body, but might each 

 require to have to some extent a different sectional area, and 

 therefore a different velocity of flow at different points of their 

 course. If we trace the streams to a sufhcient distance ahead 

 of the body, we shall there find the ocean flowing steadily on, 

 completely undisturbed by, and as we may say ignorant of, the 

 existence of the body which it will uUimately have to pass. 

 There, all the streams must have the same direction, the 

 same velocity of flow, and the same pressure. Again, if we 

 pursue their course backwards to a sufficient distance behind the 

 body, we shall find them all again flowing in their original 

 direction ; they will also have all resumed their original velocity ; 

 for otherwise, since the velocity of the ocean as a whole cannot 

 have changed, we should have a number of parallel streams 

 having different velocities and therefore different pressures side 

 by side with one another, which is an impossible state of 

 things.* 



Although, in order to get past the body, these streams follow 

 some courses or other, various both in direction and velocity, 

 into which courses they settle themselves in virtue of the various 

 reactions which they exert upon one another and upon the sur- 

 face of the body, yet ultimately, and through the operation of 

 the same causes, they settle themselves into their original direc- 

 tion and original velocity. Now the sole cause of the original 

 departure of each and all of these streams from, and of their ulti- 

 mate return to, their original direction and velocity, is the sub- 

 merged stationary body ; consequently the body must receive 

 the sum total of the forces necessary to thus affect them. Con- 

 versely this sum total of force is the only force which the passage 

 of the fluid is capable of administering to the body. But we 

 know that to cause a single stream, and therefore also to cause 

 any combination or system of streams, to follow any courses 



* In an imperfect fluid it is possible to have parallel streams having differ- 

 ent velocities and the same pressures side by side with one another, because, 

 in an imperfect fluid, change of velocity may have been communicated by 

 friction instead of by difference of pressure. 



