36o 



NATURE 



[November 25, 191 



colleges, fully two-thirds of the undergraduates who 

 would otherwise have been in residence being absent 

 on military service. The number of resident under- 

 graduates in the University of Cambridge, which was 

 3306 in Michaelmas term, 1913, fell to 1658 at Michael- 

 mas, 19 14, and a still further decline was observable 

 last term. The number was 1097 at the commence- 

 ment of the term, but many had disappeared before 

 the conclusion. A similar reduction in numbers is 

 reported, in the articles, in the Universities of Birm- 

 ingham, Bristol, Durham, Leeds, Liverpool, Man- 

 chester, and Sheflfield. To mention a few instances : 

 at Durham there are 573 students as against 947 in 

 1913-14; at Liverpool the undergraduates attending 

 classes this session number 420 and the post-graduates 

 150, while in 1913— 14 the numbers were 548 and 289 

 respectively ; at Manchester there is a decline of more 

 than 500 in the number of men students as compared 

 with 1913. 



SOCIETIES AND ACADEMIES. 

 London. 

 Royal Society, November 18. — Sir William Crookes, 

 president, in the chair. — Lord Rayleigh : The theory of 

 the capillary tube. In a recent paper Richards and 

 Coombs comment on deficiencies in the mathematical 

 treatment of the capillary tube, some of which it is 

 here attempted to remedy. In the best experimental 

 arrangement a wide and a narrow tube are connected 

 below, and the difference between the levels of the 

 lower parts of the two meniscuses is measured. In 

 the interpretation of the results for deducing the sur- 

 face-tension of the liquid, two problems arise (i) how 

 to allow for the weight of the meniscus in the narrow 

 tube, and (ii) to find what diameter is necessary for 

 the wide tube in order that the elevation due to curva- 

 ture of the liquid surface may be neglected. The first 

 problem was considered by Poisson, but his results in 

 the only really important case, viz., when the liquid 

 wets the walls of the tube, have been disputed. 

 Poisson 's formula is here confirmed and extended. 

 If r denotes the radius of the tube, h the measured 

 height of the meniscus above the truly plane level. 

 T the surface-tension, g gravity, and p the density of 

 the fluid, 2T/^•p.r = /^ + r/3-'o•I288r^//2+o•I3I2rV^^ 

 an approximation which should suffice for experi- 

 mental purposes. It may be remarked that the first 

 two terms on the right correspond to the assumption 

 of a spherical surface, which is legitimate when r is 

 small enough. A completely adequate solution of the 

 second problem is more difficult. But it is easy to 

 show theoretically that such diameters as are some- 

 times used for the wide tube (25 cm. or 3-0 cm.) are 

 quite insufficient, at any rate in the case of water, a 

 conclusion reached also by Richards and Coombs in 

 direct experiment. It appears further that the widest 

 tube used by these observers (3-8 cm.) would be in- 

 sufficient to take advantage of the actuallv achieved 

 delicacy of reading. An approximate calculation of 

 the diameter necessary for this purpose gives 4-7 cm. 

 —Prof. C. H. Lees : The effect of the form of the 

 transverse section on the resistance to the motion of 

 an elongated body parallel to its length through a 

 fluid the viscosity of which is not negligible. When 

 a very elongated body moves parallel to its length 

 through a fluid, the resistance due to the viscosity of 

 the fluid varies considerably with the form as well as 

 with the magnitude of the cross-section of the body. 

 Values of the total resistance and of the resistance per 

 unit area of contact with the fluid are given in various 

 cases. In all cases so long as the fluid is in stream- 

 line motion, the law of resistance can be expressed in 

 a simple form, and it is desirable that measurements 

 NO. 2404, VOL. 96] 



of the resistance when the motion is turbulent should 

 be made in order to determine the extent to which 

 these laws may be utilised in practical engineering.- - 

 Prof. J. Joly : A method of estimating distance at sea 

 in fog or thick weather. The method proposed is 

 based upon the different velocities of disturbances in 

 differing media. If aerial and submarine signals are 

 simultaneously emitted at a lighthouse station or light- 

 ship the lag of the aerial compared with the sub- 

 marine sound is about 4-3 seconds to the nautical mile. 

 An approaching ship picking up the signals and 

 measuring the lag to an error even of one second 

 becomes aware of her distance to less than one-quarter 

 of a mile. Similarly, wireless signals and submarine 

 signals, or wireless and aerial signals, may be used. 

 If the faster-moving signals be sent out in groups, the 

 individual signals being spaced to regular intervals — 

 say, of one second — and the slower moving signal 

 be always emitted simultaneously with the first signal 

 of a group, the navigator has onlj' to count the faster 

 signals until the slower signal reaches him, in order 

 to estimate his distance from the signal station. In 

 this case the signals themselves tell him his distance, 

 and no actual time-measurements are required on 

 board ship. It is shown that this system enables the 

 mariner to determine his position completely in all 

 circumstances which may arise. — Prof. J. Joly : A 

 method of avoiding collision at sea. This paper deals 

 with an extension of the method described in the 

 preceding paper for estimating distance at sea to the 

 problem of avoiding collision in fog. It is shown that 

 if vessels possess the means of emitting a loud and 

 crisp sound signal which can be sent out simultane- 

 ously with a wireless or a submarine signal, the deter- 

 mination of distance rendered possible thereby, along 

 with wireless information as to course and speed, will 

 enable the navigator on each ship to determine with 

 certainty (i) whether there is risk of collision or 

 whether there is no risk, and (2) the point upon his 

 own course and the moment at which collision is 

 threatened. The solution of the problem is based upon 

 the fact that at each instant the rate of mutual ap- 

 proach is the maximum if the ships are advancing so 

 as to collide. A simple p-eometrical construction, which 

 by its character is unlikely to involve error, enables 

 the mariner to solve the problem immediatelv ihe 

 signals are received. — S. W'. Richardson : The flow of 

 electricity through dielectrics. — S. Chapman : The 

 kinetic theory of gaseous viscosity and thermal con- 

 duction, and the law of distribution of molecular 

 velocities in the disturbed state. The first object of 

 the paper is to determine the velocitv-distribution func- 

 tion f{u,v,ui) in a gas in which there are small 

 variations of temperature and velocity from point to 

 point. Both simple and mixed gases are considered ; 

 the mixtures are supposed uniform, the studv of difl'us- 

 ing mixtures being deferred to a later paper. 



Zoological Society, November 9.— Dr. S. F. Harmer, 

 vice-president, in the chair. — Dr. G. E. Nicholls : The 

 anatomy of Raiia tigrina, the so-called bull-frog of 

 India. Attention was directed to certain features in 

 which this species differs from its European congeners. 

 — Dr. J. C. Mottram : Pattern-blending with reference 

 to obliterative shading and concealment of outline. 

 The paper recorded the results of laboratory experi- 

 ments with artificial patterns. The experiments 

 showed that obliterative, or counter-shading, could be 

 produced by blended black-and-white pattern, and that 

 beyond the blending distance, interruptions at the 

 margin of a pattern, or similarly placed eye-spots, blur 

 the margins. The laboratory experiments were com- 

 pared with actual patterns of animals. — Dr. J. C. 

 Mottram : The distribution of secondary sexual char- 

 acters amongst birds, with relation to their liability to 



