632 



NATURE 



{Oct. 25, 1883 



Darcy's pipes were not uniform between the gauge points, the 

 sections varying as much as 20 per cent., and the temperature 

 was only casually given. These matters rendered a close agree- 

 ment unlikely ; it was rather a question of seeing if there was 

 any systematic disagreement. When the curves came to be 

 shifted, the agreement was remarkable ; in only one respect was 

 there any systematic disagreement, and this only raised another 

 poiDt ; it was only in the slopes of the higher portions of the 

 curves. In both my tubes the slopes were as 1722 to I ; in 

 Darcy's they varied according to the nature of the material, from 

 the lead pipes, which were the same as mine, to I 92 to I with 

 the cast iron. This seems to show that the nature of the surface 

 of the pipe has an effect on the law of resistance above the 

 critical velocity. 



16. The Critical Velocities. — All the experiments agreed 



I P 



in giving v 1 = — - as the critical velocity, to which correspond 



278 D 

 as the critical ^pressure i e 



ps 



the units being metres 



47700000 D 3 



and degrees Centigrade. It will be observed that this value is 

 much less than the critical velocity at which steady motion broke 

 down. 



17. General Law of Resistance. — The log. homologues all 

 consist of two straight branches, the lower branch inclined at 

 45°, and the uppe' one at « horizontal to 1 vertical, except for 

 the small distance beyond the critical velocity these branches 

 constitute the curves. These two branches meet in a point, O, 

 on the curve at a definite distance below the critical pressure, so 

 that, ignoring the small portion of the curve above the point 

 before it again coincides with the upper branch, the logarithmic 

 homologues give for the law of resistance for all pipes and all 



D 3 / D \ n 



velocities A — i = IB —v \ , where n has the value unity as 



long as either member is below unity, and then takes the value 

 of the slope « to 1 for the particular surface of the pipe. 



If the units are metres and degrees Centigrade — 

 A = 67,700,000 

 B = 39 8 

 P = 1 + 0-0336 T + O-00O22I T 2 . 



This equation then, excluding the region immediately about 

 the critical velocity, gives the law of resistance in Poiseuille's 

 tubes, those of the present investigation, and Darcy's, the range 

 of diameters being, from 0000013 metres (Poiseuille, 1843), to 05 

 metres (Darcy, 1857) ; and the range of velocities from o - O026 

 to 7 metres per sec, 1883. 



This algebraical formula shews that the experiments entirely 

 accord with the theoretical conclusions. The empirical constants 

 are A, B, P, and « ; the first three relate solely to the dimen- 

 sional properties of the fluid which enter into the viscosity, and 

 it seems probible that the last relates to the properties of the 

 surface of the pipe. 



Much of the success of the experiments is due to the care and 

 skill of Mr. Foster of Owens College, who has constructed the 

 apparatus and assisted me in making the experiments. 



SOCIETIES 



AND ACADEMIES 

 Paris 

 Academy of Sciences, October 15. — M. Blanchard, presi- 

 dent, in the chair. — Note on a formula of Hansen in connection 

 with the mechanism of the heavens, by M. F. Tisserand. — On the 

 measurement of the forces brought into play in the various ac- 

 tions of human locomotion (continued), three illustrations, by 

 M. Marey. By combining the indications obtained from the 

 dynamometer with those yielded by instantaneous photography, 

 a continuous comparison may be made of the forces brought 

 into action with the movements resulting from them. The 

 various applications of these two methods will form the subject 

 of future experiments. — On a memoir by M. Raoult, entitled : 

 " Loi generate de Congelation des Dissolvants," — report by 

 MM. Cahours, Berthelot, and Debray. Water holding saline 

 bodies in solution freezes at a lower temperature than pure water, 

 and the English physicist Blagden had shown in 1788 that the 

 lowering of the freezing-point due to this cause is in many cases 

 in proportion to the quantity of matter held in solution. This 

 principle is now generalised by M. Raoult, who arrives at the 

 conclusion that the freezing-point of any liquid compounds 

 capable of solidification is lowered by all solid, fluid, or gaseous 

 bodies dissolved in them. The reporters agree with the author 

 that his methods will be found useful in supplying new means for 



ascertaining by a simple process the degree of purity of given 

 substances. — Trial trip of an electric screw balloon made by 

 MM. A. and G. Tissandier, note by M. G. Tissandier. This 

 preliminary experiment took place at Auteuil on October 8, and 

 was attended by a certain measure of success, although the ap- 

 paratus proved powerless to prevent the spinning motion of the 

 balloon when heading against aerial currents. The trip will be 

 renewed as soon as certain improvements have been made in 

 the electromotor suggested by this experiment. — Studies made on 

 the summit of the Pic du Midi, with a view to the establishment 

 of a permanent astronomic station, note by MM. Thollon and 

 Trepied. — On the transformation of certain equations of the 

 second degree to two independent variables, and on some inte- 

 grations thence deducible, by M. R. Liouville. — On a method 

 of isolating the calorific from the luminous and chemical rays, 

 by M. F. van Assche. — On the form and characters of the 

 reflex muscular contraction, by M. H. Beaunis. — On the resisting 

 power of a ring whose outer surface supports a normal pressure 

 con-tant as to unity of length of its mean axis, by M. J, 

 Boussinesq. — On surfaces whose total curve is constant, by M. G. 

 Darboux. — Indices of refraction of fluate of lime for the rays of 

 different wave-lengths as far as the extreme ultra-violet, by M. 

 Ed. Sarasin. — Note on a new method of insulating the metallic 

 wires used in telegraphy and telephony, by M. C. Widemann. — 

 Note on the determination of the equivalents of metals by means 

 of their sulphates, by M. H. Baubigny. — On the process at 

 present employed to determine the glucose in cane-sugar, by 

 M. P. Lagrange. The object of this paper is to show that the 

 quantitative analysis of glucose, made on a liquor whether 

 treated or not with subacetate of lead, is liable to serious errors. 

 — Analysis of a specimen of guano from the Cape ^erde 

 Islands, byM. A. Andouard. — Zoological dredgings and thermo- 

 metric soundings in the lakes of Savoy, by M. F. A. Forel. — On 

 the organisation of the Spadella Marioni, a new species from the 

 Gulf of Marseilles, by M. P. Gourret. — On some peculiarities 

 in the structuro of Tunicata, by M. L. Roule. — Fresh studies 

 on the fossil ruminants of Auvergne, by M. Deperet. — On the 

 treatment of strabismus by means of the capsular "advance- 

 ment," by M. L. de Wecker. — On the part played by the 

 ligneous vessels in the upward movement of the sap, by M. J. 

 Vesque. — Note on a lunar mirage observed on the night of 

 October 11, by M. Virlet d'Aoust. 



CONTENTS page 



A Scientific Catalogue 609 



The Fisheries of the Adriatic 609 



Our Book Shelf:— 



Swinburne's "Practical Electrical Units Popularly 



Explained " 610 



Day's " Fishes of Great Britain and Ireland" . . . 61 1 



Greene's " Parrots in Captivity " 61 1 



"Voyages of G. S. Karelin on the Caspian Sea". . 611 

 Letters to the Editor : — 



The Green Sun. — Rev. W. R. Manley ; Henry 



Cecil 611 



Snake Poison. — Mrs. Catherine C. Hopley . . . 612 

 Simultaneous Affections of the Barometer. — A. N. 



Pearson 612 



Table of Different Velocities.— H. Baden Pritchard 612 



Oswald Heer 612 



The Backward State of Chemistry in England . . 613 



The Cholera Bacillus 614 



National Traits in Science 614 



The Geodetic Congress 616 



Large and Rude Palaeolithic Implement. By Worth- 



ington G. Smith {With Illustration) 617 



Agriculture, its Needs and Opportunities. By Prof. 



John Wrightson 618 



The Great Nebula in Orion (IVith Illustrations) . . 619 



Notes 621 



Our Astronomical Column : — 



Pons' Comet 624 



The Great Comet of 1882 624 



The Variable Star U Cephei 625 



Physical Notes 625 



The Great Tidal Wave. By Prof. G. H. Darwin, 

 F.R.S., and Major A. W. Baird ; David Gill; C. 



Meldrum, F.R.S. {With Diagram) 626 



The Motion of Water. By Prof. Osborne Reynolds, 



F.R.S. 'With Diagrams) 62 ? 



Societies and Academies 63^ 





