48o 



NATURE 



{Sept. 15, 1887 



Dwight. In this paper (No. 6 of the series) the author deals 

 with the discovery of additional fossiliferous Potsdam strata 

 and pre- Potsdam strata of the Olenellus group near Pough- 

 keepsie. This review of the latest palaeontological facts makes 

 it evident that the strata in Dutchess County are simply the 

 continuation of the strata characterizing the Taconic and ad- 

 joining series lying northward. But while proving a grand 

 unity, they indicate also an interesting and unexpected variety 

 of rock structure. — Image transference, by M. Carey Lea. By 

 image transference are here denoted curious effects produced on 

 sensitive films, and specially interesting in connexion with the 

 subjects of papers which appeared in the May and June num- 

 bers of the journal. In supplement to those papers the possibility 

 is here shown of developing on a film of silver haloid a complete 

 image, a print from a negative for example, without either 

 exposing the silver haloid to light, or to the action of hypo- 

 phosphite, or subjecting it to any treatment whatever, between 

 the moment of its formation and that of its development. The 

 film of silver haloid comes into existence with the image already 

 impressed upon it. — The theory of the wind vane, by George E. 

 Curtis. The author's theoretical studies lead to the inference 

 that the oscillations of both spread and straight vanes are smaller 

 as the vanes are longer and larger ; that the spread is always 

 more stable than the straight vane ; and that this advantage in 

 stability is greater for long than for short vanes, and is inde- 

 pendent of the wind velocity. — On the manner of deposit of the 

 glacial drift, by O. P. Hay. The author's studies of this great 

 geological problem lead to the following conclusions : (i) an ice- 

 sheet moving over a nearly level surface would possess far less 

 abrading power than it would have while descending at a higher 

 angle ; (2) through subsidence of the glacial mass by the earth's 

 heat and other causes a constantly increasing proportion of inert 

 matter would collect in the lower-layers of the moving ice ; (3) 

 this accumulated material would tend to retard and finally arrest 

 the motion of the lower portions of the glacier, and a per- 

 manent deposit would then be gradually made ; (4) other de- 

 tritus might accumulate at the foot of the glacier as a terminal 

 moraine, and still other masses on the top of the already 

 formed deposit when the glacier finally melted. 



SOCIETIES AND ACADEMIES. 



Paris. 



Academy of Sciences, September 5. — M. Herve Mangon 

 in the chair. — Photochronography applied to the dynamic 

 problem of the flight of birds, by M. Marey. Having in a 

 previous note shown that the kinematics of flight may be com- 

 pletely illustrated by photochronography, the author here proves 

 that the same process contains all the elements necessary for 

 solving the dynamic problem of flight ; that is to say, for mea- 

 suring the muscular forces and the work performed by the bird. 

 Here is applied the mechanical principle that, if the mass of a 

 body and the movements animating it be known, it is possible 

 to deduce the value of the forces by which those movements are 

 produced. On the photochronograph are measured all the dis- 

 placements of the mass of the bird on the wing, together with the 

 velocities of these movements. On the other hand the weight, that 

 is, one of the forces to which the mass is submitted, is also known, 

 while the resistance of the air, another of these forces, may be 

 determined experimentally. Consequently the unknown quantity 

 to be eliminated will be the muscular force of the bird with its 

 momentum of action, and the value of its two components, one 

 acting vertically against the weight, the other horizontally 

 against the inert resistance of the mass and of the air. In these 

 experiments the displacements of the bird are successively mea- 

 sured according to these two vertical and horizontal elements. — 

 Measurement of luminous sensations in function of the quantities 

 of light, by M. Ph. Breton. Since the invention of Bouguer's photo- 

 meter It is known that if a dull white surface be disposed in con- 

 tiguous zones receiving equi-different quantities of light, the percep- 

 tible contrasts between such zones are very far from being equal. 

 To explain this phenomenon it has been suggested that the eye 

 perceives the relation between two contiguous lighted surfaces. 

 But the law (attributed to Fechner and Weber) based on this 

 assumption— to the effect that, if several contiguous luminous 

 surfaces are in geometrical progression, the sensations of the 

 contrasts are equal— is shown to be incorrect by the experiment 

 here described.— Observations of Brooks's new comet, made at 

 the Observatory of Algiers with the o'So-metre telescope, by 



MM. Trepied, Rambaud, and Sy. — Observations of the same 

 comet made at the Observatory of Lyons with the 6-inch 

 Brunner equatorial, by M. Le Cadet. The positions of this 

 comet for August 29 and 30 and September i are also given 

 from measurements taken by M. Gruey at the Observatory 

 of Besan9on. Its brightness is that of a star of the tenth mag- 

 nitude. — Differential formulas for the variation of the elements 

 of an orbit, by M. R. Radau. To correct a provisional system of 

 elements it is often preferable to have recourse to the equations 

 supplied by the ephemerides, rather than repeat the direct calcu- 

 lation of the elements. But the method is somewhat laborious, 

 as the equations generally include six unknown quantities. The 

 author, however, here shows that it is possible to give them a 

 form in which the number of unknown quantities will be dimin- 

 ished without causing any complication in the calculation of the 

 coefficients. — Note on M. Bertrand's problem, by M. Desire 

 Andre. A direct solution is given of this problem, followed by 

 some remarks by M. Bertrand himself, pointing out its applica- 

 tion to the question of chances in games of hazard as treated by 

 Huygens, Moivre, Laplace, Lagrange, and Ampere. He offers 

 a fresh solution of the problem : if a player stake the «th part 

 of his fortune and continue the game indefinitely, what is the 

 probability of his being ruined within a given number of rounds? 



BOOKS, PAMPHLETS, and SERIALS RECEIVED. 



A Revised Currency System ; H. Bull (Hamilton). — Laws and Definitions 

 connected with Chemistry and Heat : R. G. Durrant (Rivingtons). — Educa- 

 tional Ends : S. Bryant (Longmans). — Challenger Report, Zoology, vol. xx. 

 (Eyre and Spottiswoode). — A Short Introduction to the Study of Logic : 

 L. Johnstone (Longmans). — The Instability of Gold as a Standard of Value : 

 H. Bull (Hamilton).— The Eruption of Tarawera. N.Z. : S. P. Smith (Wel- 

 lington). — The Icerya or Fluted Scale (^Vashington). — U.S. Department of 

 Agriculture, Division of Entomology, Bulletins No. 13 and 14 (Washington). 

 — Kryptogamen-Flora von Schlesien, iii. Band, 3 Liefg. (Kern, Breslau). — 

 Beiblatter zu den Annalen der Physik und Chemie, 1887, No. 8 (Barth, 

 Leipzig). 



CONTENTS. PAGE 



A Batch of Guide-Books to the Norfolk Broads . . 457 

 Our Book Shelf :— 



" Connaissance des Temps " 459 



Todhunter : " A Treatise on Analytical Statics " . . 459 

 Letters to the Editor : — 



Measurements of the Heights and Motion of Clouds in 



Spitzbergen. — Dr. Nils Ekholm 459 



Occurrence of Apatite in Slag. — W, M. Hutchings . 460 

 Electricity of Contact of Gases with Liquids. — ^J. 



Enright 460 



Cocoa-nut Pearls.— Dr. J. G. F. Riedel 461 



Stars with Remarkable Spectra. I. {Ilhistrated) . . 461 

 The British Association : — 



Section D. — Biology. — Opening Address by Alfred 

 Newton, M.A., F.R.S., F.L.S., V.P.Z.S., &c.. 

 Professor of Zoology and Comparative Anatomy in 

 the University of Cambridge, President of the 



Section 462 



Section E. — Geography, — Opening Address by 

 Colonel Sir Charles Warren, R.E., G.C.M.G., 

 F.R.S., F.R.G.S., President of the Section ... 465 

 Section G. — Mechanical Science. — Opening Address 

 by Prof. Osborne Reynolds, M.A., LL.D., J| 

 F.R.S., M.Inst. C.E., President of the Section . 48 



Notes 4^ 



Our Astronomical Column : — 



The Neuchatel Observatory 477 



The Wedge Photometer 477 



Brooks's Comet 47?" 



Astronomical Phenomena for the Week 1887 ^ 



September 18-24 47^ 



Geographical Notes 47^ 



Grants for Science and Art Instruction 47 



Scientific Serials 47 



Societies and Academies 4^ 



Books, Pamphlets, and Serials Received 4^ 



