468 



NA TURE 



[September 15, 1898 



We have only to consider a narrow band of fluid adjacent to 

 the surface which may be considered flat ; the mean motion is 

 in the direction of the surface, and the fluid is in mean equili- 

 brium in direction perpendicular to the surface. 



Taking u for the mean flow, and w for the relative motion 

 perpendicular to the surface. 



Then, by the laws of motion, we have, p being the density if 



2 is distance from the surface, — {p + pvfl) = o. 

 dz 



Now vfi is the square of the normal component of sinuous 

 motion, which rapidly increases from zero at the surface, hence 

 the fall of pressure from the surface is measured by the rate of 

 increase of fw^. 



With this interpretation the facts shown by the light bands 

 adjacent to the solid, afford not only a very interesting verifica- 

 tion, but also an instructive addition to the methods of demon- 

 strating the actions in fluid. 



With respect to the photographs with the air, as indicating the 

 character of sinuous flow ; these, I think, are entirely confused 

 by the motion of the air through the water, and are far inferior to 

 what has been obtained with colour bands of equal density. 



The more recent of your experiments (made after my method 

 of colour bands) are in many respects similar to those which I 

 exhibited with the lantern first at the Royal Institution in a 

 Friday evening lecture "On the two manners of motion of 

 water " in 1884, and which I have since elaborated for demon- 

 stration in the College. They are strictly conformable to the 

 theory of the motion of viscous fluids as given in the papers on 

 the Theory of Lubrication {Phil. Trans. R.S., 1886, part i.), 

 and on the Theory of Viscous Fluids, already referred to. But 

 although I had applied the theory to the flow of fluids between 

 parallel surfaces very close together, I had not studied the flow 

 between such surfaces round obstructions, and it was with much 

 interest that I saw the beautiful photographs of the stream lines, 

 realising as I did at once that .the velocities must have been so 

 small compared with the critical velocities that the inertia was 

 of no account, so that the pressure would vary only along the 

 lines of flow, while since the surfaces were parallel, / being 



pressure, ti and v mean component velocities, ^ = - cu, 



dx 

 dp 

 ^ = - cv, and hence p became the potential function of the 



mean flow which, therefore, corresponded (geographically but 

 not dynamically) to the ideal flow of a perfect fluid. (The same 

 explanation of this coincidence is given in the copy of Sir 

 George Stokes' paper). The coincidence is theoretically inter- 

 esting. But as the domination of the effects of inertia by 

 viscosity in the experiments is only obtained by reducing the 

 mean velocity far below the critical value, the results cannot 

 imply any such domination beyond that which breaks down 

 when the critical value is reached, and therefore cannot imply 

 any finite layer of fluid not subjected in some degree to sinuous 

 motion. Yours truly, Osborne Reynolds. 



Prof. Hele Shaw. 

 September 4. 



Magnetic Storm. 



In view more especially of the present sitting of the Inter- 

 national Conference on Terrestrial Magnetism at Bristol, it is 

 of interest to note the occurrence of a' fairly sharp magnetic 

 storm on the afternoon and evening of Friday, September 9. 

 It was associated presumably with the aurora simultaneously 

 seen in England. 



On the night of September 2 and morning of September 3 

 there was a very appreciable though much smaller disturbance ; 

 but subsequent to that the magnetic curves were quiet, especially 

 so on the 6th, 7th, and morning of the 8th. The principal dis- 

 turbance commenced somewhat gradually about noon on the 

 9th ; but one of its most striking features, as recorded at Kew 

 Observatory, was an exceptionally rapid fall occurring simul- 

 taneously, at 3.5 p.m., in the horizontal and vertical forces and 

 in the westerly declination. The fall was so rapid as to be 

 shown somewhat indistinctly on the photographic traces ; 

 but it amounted to at least 1 5' in the declination, and -0023 

 C.G.S. units in the horizontal force. The recovery from this 

 fall was also rapid. 



The declination needle between 5.15 p.m. and 8.8 p.m. 

 receded 54' to the east, then turned, and in the course of the 

 next 32 minutes moved 59' to the west. 



NO. 1507, VOL. 58] 



The horizontal force attained its extreme maximum and 

 minimum at 2.42 p.m. and 8.30 p.m. respectively, the range 

 amounting to -0050 C.G.S. units (or about 1/37 of the whole 

 component). Between 7.30 and 8.30 p.m. this element fell 

 •0036 C.G.S. units. The vertical force reached its maximum 

 about 6 p.m. and its minimum about 8.30; but as the trace 

 unfortunately got off the sheet near the minimum, one can only 

 say that the range of vertical force exceeded '0036 C.G.S. units. 



The curves had become fairly quiet by midnight of the 9th ; 

 but there was a recrudescence of the disturbance between 8 a.m. 

 and midnight of the loth, and subsequent smaller movements 

 occurred on the nth. Charles Chree. 



Kew Observatory, September 12. 



Lilienfeld's Synthesis. 



The interesting article in your issue of August 18, signed by 

 Dr. Sidney Williamson, ably summarises the position of affairs 

 as regards the various attempts that have been made towards 

 the synthesis of proteids. There is one point, however, which 

 may possibly require modification. Dr. Williamson states 

 "Such colour tests as Millon's, nitric acid. Sac, have no real 

 value ; the colour developed may be due to the proteid mole- 

 cule as a whole, but more probably to some decomposition 

 product, and, as already mentioned, some colloids which 

 bear no relation to actual proteids give reactions considered 

 characteristic of these substances." 



Having devoted considerable attention to the colour reactions 

 of proteids and their derivates, I may state that there is every 

 probability that all the colour reactions are due to disintegration 

 of the proteid molecule during the reaction. Full details of 

 this work will be found in a paper I published in Xh^ Journal of 

 Physiology in 1894. There are ten more or less trustworthy colour 

 reactions given by proteids, and I am unaware of any colloid 

 that is not related to a proteid which will give more than two 

 of these reactions, and there is at present no known colloidal 

 substance which will produce the intravascular coagulation of 

 the blood, except the substances synthesised by Grimaux and 

 myself, and nucleo-proteids derived from the animal organism. 



Although some of the substances I have synthesised give all 

 the colour reactions of proteids, I do not think they are pro- 

 teids ; indeed, they are probably far from it, and until an 

 absolutely trustworthy test for a proteid is discovered, and the 

 molecular constitution of albumen is known, it is premature to 

 assert that any synthesised substance is a proteid. To show 

 the fallacy of relying solely on colour reactions, I may mention 

 that a mixture of tyrosine, indol, and biuret will give all the 

 colour tests considered diagnostic of proteids. There is little 

 doubt that Lilienfeld's substance is an addition to those already 

 made by Schiitzenberger, Grimaux, and myself, but for the 

 reasons above stated I do not think there is any trustworthy 

 evidence that it is actually pepton. 



Sandridge, Eltham, Kent. John W. Pickering. 



Larvae in Antelope Horns. 



I AM much interested in the article upon horn-feeding larvae 

 which appears in the last number of Nature, just received by 

 me (June 9). 



It may interest your readers to have additional assurance that 

 the living horns are attacked and infested with the larvse in 

 question, for cocoons and pupre have been extracted from such 

 horns within an hour or two of the killing of the animal owning 

 them. This I am able to state on the unimpeachable authority 

 of an officer who made the observation. 



I myself have removed the cocoons and empty pupa cases, 

 half extended from the orifice of the burrow in the horn ; but 

 the horns so affected had been dead for some weeks ; and I 

 have not, so far, had the opportunity of examining freshly killed 

 specimens, nor of seeing the living larvae. 



I enclose a few of the empty cocoons and pupa cases, extracted 

 by me from the diseased horns — for a disease it must be con- 

 sidered — from the antelope's point of view ! 



Lagos, July 22. Henry Strachan. 



This letter is of unusual interest, as it now clears up a point 

 which has been long in doubt. In my article to Nature which 

 appeared on June 9 last, I gave a short account of the habits of 

 horn-feeding larvae, and since that time, having obtained addi- 

 tional notes, I beg to submit the following remarks. I have 

 carefully examined the cocoons sent by Mr. Strachan, and un- 



