426 



NA TURE 



[August 30, 1894 



a thin stiff plane caused to move at sixty miles an hour through 

 it, in a direction inclined to the plane at a slope of about one 

 in eight, was found to be about fifty-three times as great as the 

 estimate given by th= old "theorelical " (!) formula, and some- 

 thing like five or ten times that calculated from a formula 

 written on the black-board by Lord Rayleigh, as from a 

 previous communication to the British Association at its 

 Glasgow meeiing in 1S76. 



I had always lelt that there was no validity, even for rough 

 or probable estimates, in any of the "theoretical " investigations 

 hitherto published : but how wildly they all fall short of the truth 

 I did not know until I have had opportunity in the last few 

 days, frocul negoliis, to examine some of the observational 

 results which Maxim gave us in the introduction to his paper. 

 On the other hand, I have never doubted but that the true 

 theory was to be found in what I was taught conversationally by 

 William Froude twenty years ago, and which, though I do not 

 know of its having been anywhere published hitherto, is clearly 

 and tersely expressed in the following sentence which I quote 

 Irom a type-written copy, kindly given me by Mr. Maxim, of 

 his paper of last week : — 



" The advantages arising from driving the aeroplanes on to 

 new air, the inertia of which has not been disturbed, is clearly 

 shown in these experiments." 



Founding on this principle, I have at last, I believe, suc- 

 ceeded in calculating, with some approach to accuracy, the force 

 required to keep a long, narrow, rectangular plane moving 

 through the air with a given constant velocity, \', in a direction 

 perpendicular to its length, /, and inclined at any small angle, ;, 

 to its breadth, a. In a paper, which I hope to be able to com- 

 municate to the Philosophical Magazine in time for publication 

 in its next October number, I intend to give the investigation, 

 including consideration of "skin-resistance" and proof that it 

 is of comparatively small importance when / is not much less 

 than I 10, or i 20, of a radian, and the "plane" is of some 

 practicably smooth, real, solid material. In the meantime, here 

 is the result, with skin-resistance neglected : — The resultant force 

 (perpendicular, therefore, to the plane) is 2»V'- sin 9 cos 9 la ; 



which is 47'^"1'_ times (or for the case of sin 9 = S, one hundred 



sin 9 

 times), the old miscalled "theoretical" result. Kelvin. 



Eastern Telegraph Company's Cable Steamer 

 Eltctra ; crossing the mouth of the Adriatic, 

 August 17. 



Geological Maps of Baden. 



It may interest some of your readers likely to visit the Black 

 Forest, that Herr Winter, of Heidelberg, has begun the issue of 

 an official series of geological maps, each 19A x 17A inches, with 

 memoir. Two are already out, one east of Heidelberg, the 

 other giving the Mooswald district, north-east of Gengenbach. 

 The scale is I ; 25000 ; i.e. 10 cm. to 2ikm., or practically two 

 and a half inches to the mile. Three sections are given on the 

 sheet; the memoir has about 100 pages. The price for the map 

 and memoir is only two marks ; if the map is mounted, three 

 marks. I had intended to comment on the contrast between 

 this marvellous cheapness and our own Survey issues, as our inch 

 ordnance cannot approach this for detail ; for instance, the 

 contour lines are given for every ten metres. IJut a paragraph 

 read to-day in the New York Nation of August 9, in a letter 

 signed " W. M. I )." will speak for me : — ". . . unfortunately 

 Ihe publications of the liritish Surveys are rarely found complete 

 at home outside of the Governmental bureaus in Washington. 

 Very few copies of the liritish geological reports and maps are 

 presented to libraries in foreign countries, and the prices at 

 wtii. (1 ihey are sold practically forbids their purchase. The 

 . , arc, moreover, coloured by hand, so every copy Is 

 <.Alji.ii»ive ; while ours are lithographed, and ' additional copies ' 

 arc of only nominal cost, perhaps three or four cents apiece. . . . 

 The British practice almost seals up the cosily results of Ihe 

 geological surveys. ... It was a satisfaction to learn that 

 I his opinion, formed at home, was shared and emphatically 

 ivcrhcre"(al Kdinburgh). 

 -n Stale geology maps are also, of course, lilho- 

 ^i..{ .,. ., ..,,1 so are the equally cheap Imperial mips of all 

 Germany, anotlitr ticries, now being published byjuslus Perthes, 

 and of which aKo the first two arc lusl issued and cover the 

 same region, South-west Germany. Th.it the policy pays seems 

 tertain. Three other purchases, for instance, were the 



NO. 1296, VOL. 50] 



immediate result of my own, whereas my friends have always 

 been content to borrow my English maps, when I could see 

 my way to lend them. J. Edmijnd Clark. 



Vork, August 21. 



Variation of " Aurelia." 



I SEE that you note (p. 413) the occurrence of an .liirelia with 

 pentamerous symmetry. In an expedition of the Liverpool 

 Biological Society to Ililbre Island, a few weeks ago, we found 

 several such specimens, and remarked upon the frequen cy of 

 the variation. I think the number was either four or five 

 pentamerous forms out of twelve examined. 



Port Erin, August 25. W. A. Herdman. 



CREATURES OF OTHER DAYS.^ 



CREATURES of Other Days" is a work of literature 

 rather than science, and is yet so full of reference 

 to scientific facts and discoveries that it appears like a 

 work of learning. It narrates the history of extinct 

 animals laboriously discovered, and in many cases still 

 undergoing laborious interpretation by paUeontologists, 

 in language which is free from technicality. There is no 

 reference to the anatomical structure of the skeleton 

 which necessitates technical language. There is no 

 critical digest of the facts enumerated, or of the nomen- 

 clature under which the fossils are described. No 

 attempt is made to state the osteological characters 

 which distinguish these fossils from each other. Mate- 

 rials which any author has supplied are accepted im- 

 partially, and the same animal type is illustratetl by 

 dissimilar restorations. Thus Mr. Hulke made a quadru- 

 pedal restoration of Hypsilopltodon Foxi, an animal which 

 once was termed a young Iguanodon, out of which Mr. 

 Smit has restored a vigorous-looking lizard. If these 

 interpretations are correct, it is improbable that the 

 vertical bipedal restoration of Aiichisaiirus, given by 

 Prof. Marsh, and restored by Mr. Smit, can also be 

 satisfactory. Many of the original restorations endea- 

 vour to convey an idea to the unlearned of the skin and 

 aspect of the living animals. .\nd as these are b.ised 

 upon published figures, or restorations, the author has no 

 doubt gone to the best material which was available, even 

 when the result is unsatisfactory. Sir William Flower, in 

 his pref.ace, fairly states the claim of the restorations to 

 consideration. He says : " In the restoration of the 

 external appearance of extinct animals, known only by 

 bones and teeth, there is much of imagination, much 

 indeed of mere guess work, and I should therefore be 

 sorry to guarantee the accuracy of any of the representa- 

 tions of animals in this book, the majority of which were 

 never seen in the flesh by the eyes of mortal man. I 

 think, however, I may safely say that Mr. Hutchinson 

 and his accomplished artist, Mr. Smit, have done their 

 work carefully and conscientiously, and given us, in most 

 cases, a fair idea of the appearance of the creatures they 

 have endeavoured to depict according to the best evidence 

 at present available." Sir William commends the figures 

 because they give a better idea of the animals than most 

 persons who only saw their fossil remains would be able 

 to carry away. This unscientific attitude of the book is 

 its chief merit. It is only when the author becomes .in 

 expositor of science that scientific men are likely to 

 disagree with him. More care was needed in some of 

 the restorations. The old red sandstone fishes, for 

 example, are drawn without any regard to their relative 

 sizes, those of the upper and lower beds swimming 

 together as though they were of the same geological 

 age, while at the bottom of the water are Trilobites, 

 lirachiopods, and Cephalopods, which no one ever saw 

 in the old red sandstone. 



' By Rev. H. N. Hutchinson, U.A., F.G.S., author of '' Eiclincl 

 Moniicrs." Willi iiumcroiis illuslrjlions by J. Smit and others. (London ! 

 Chapman and Hall, Limited, i8>y4.) 



