June 13, 1907] 



NATURE 



i.Si 



to suitable axes) is everywhere zero — at least so far as 

 electromagnetic phenomena are concerned. 



Though I find myself in agreement with Prof. Richard- 

 son's conclusion that magnetic intensity is not to be 

 identified with speed of ;ctheroal flow, as explained in his 

 letter to Nature of May 23, I venture to dissent from his 

 arguments. These proceed from the contention that, on 

 the contested assumption, certain integrals would become 

 infinite. Now, in the first place, it appears to me from 

 mere inspection that both these integrals (which I have 

 not actually evaluated) are in reality finite ; in the second 

 place, neither integral expresses a magnitude which bears 

 directly on the point at issue, one of them being justly 

 crittcised by Sir Oliver Lodge in N.ature of June 6 as 

 apparently devoid of mathematical meaning. The question 

 proposed is as to the momentum due to an electric charge 

 upon a moving sphere, and in this connection the really 

 significant magnitude is the kinetic energy, expressed in 

 terms of the translational velocity. Differentiating this 

 expression with respect to the velocity, we have at once 

 the momentum, the result obtained being independent of 

 anv physical theory as to the ultimate nature of the energy 

 in a magnetic field. C. V. Burton. 



Cambridge, June 8. 



Decomposition of Radium Bromide. 



Yesterd.w, on opening a glass tube containing i milli- 

 gram of radium bromide which had been hermetically 

 sealed for almost exactly twelve months, there was a very 

 strong odour of bromine which hung about the tube for 

 about ten minutes. The amount of the bromide decom- 

 posed in this period would be about 5-4x10-" grams 

 according to Rutherford ; the amount of bromine corre- 

 sponding to this would be about 2X10-' grams. Perhaps 

 some chemist could say definitely whether this amount of 

 bromine would be detectable by its odour. The volume of 

 the tube was about 4 cubic centimetres. 



Alfred W. Porter. 



University College, London, June 8. 



The Mass of the a Particle. 



Apparently the following simple and obvious method of 

 calculating the mass of the a particle has been overlooked. 



.\ccording to Rutherford, the number of o particles 

 emitted per second by a gram of pure radium is 2.5x10". 

 Of these particles, one-quarter comes from each of the 

 four elements Ra, RaEm, RaA, RaC. The particles from 

 these four elements are emitted with velocities 0-82 V„, 

 0-87 V;,, 0.90 V,, I 00 V„ respectively, where V, is 

 2-6x10' cm. /sec. ; they all cease to produce ionisation 

 when their velocity is 045 V„. Hence the loss of kinetic 

 energy of all the a particles emitted from one gram of 

 radium in passing over their ionising ranges is 



2;52<Jo" ^ ^^^^ ^ {(0-82)2-1- (0-87 )■- + (0-90)24- 12- 4 ^ 



(0-431-1(2-6 X ioS)2 = « X 5-3 X io2», 



where m is the mass of an o particle. 



At the same time, it is known that one gram of radium 

 gives out 105 gram-calories per hour (mean value), or 

 1-22x10" ergs per second. If we may identify this 

 quantity of heat energy with the kinetic energy lost by the 

 o particles in ionisation we have 



niX5-3X 10°' = 1-22 X 10' 

 or 



ii; = 2-3X 10--'. 

 The ratio e/m for the a panicle is 1-56x10" electro- 

 static units. The two most probable theories of the nature 

 of the a particle are (i) that it consists of an atom of 

 helium carrying a charge 2€, where c is the electronic 

 charge 3-4X io-'°, and (2) that it is a molecule of hydrogen 

 carrying a charge €. On the hypothesis (i) the mass of 

 the particle is 4.26x10--"'; on the hypothesis (2) it is 

 2.13X10--'. The calculation given indicates that (2) is 

 correct, and explains the failure of Greinacher and Kern- 

 baum to obtain helium from the a rays of polonium {Phys. 

 Zeit., 1907, p. 339). 



NO. 1963, VOL. y6] 



If it be assumed that the whole of the kinetic energy 

 of the a particles, and not only that part of it which is 

 spent in ionisation, appears as heat energy, the value for 

 m is found to be 



1-78x10-=''. 

 I have thought it best to give the maximum estimate of 

 that quantity which can be attained by this method. 



Norman R. Campbell. 

 Trinity College, Cambridge, June 3. 



The "Renal-portal System" and Kidney Secretion. 

 I recently published a short paper (Proc. Zool. Soc, . 

 1906) on the significance of the so-called " renal-portal 

 system " found in most of the lower Vertebrata. In this 

 paper I advanced strong reasons for supposing that the 

 " renal-portal system," or, as I prefer to call it, renal 

 cardinal meshwork, is non-excretory in nature. I showed 

 that, both developmentally and structurally, there was 

 every reason to doubt whether the renal cardinal mesh- 

 work takes any part in the formation of the plexus of 

 blood-vessels which surrounds the urinary tubules (although, 

 of course, these are connected with each other), and that 

 therefore the blood apparently supplied to the kidney by 

 the '* renal-portal " (post-renal) vein is in all probability 

 not utilised in the production of the kidney secretion. This 

 conclusion, opposed to that held by most physiologists and 

 morphologists, I supported by citing the physiological ex- 

 periments of Nussbaum (Pfliiger's Archiv. xvi., xvii., 1878; 

 Aiiat. Anzeig., i., 18S6) and Beddard (yowr. Physiol., 

 xxviii., 1902), which afforded valuable confirmation. These 

 experiments, as is well knpwn, proved that after the 

 arterial supply of the frog's kidney had been eliminated 

 all secretion immediately stopped, notwithstanding the facts 

 that the " renal-portal " circulation was still in full swing 

 and that powerful diuretics were employed. The sole 

 objection to regarding these experiments as conclusive was 

 that, in consequence of the kidney being deprived of 

 oxygenated blood, the tubular epithelium had degenerated, 

 and was therefore not in a condition to secrete. While 

 recognising this objection, yet for the other reasons which 

 I had already advanced I ventured to maintain that, ever* 

 if the blood in the post-renal vein could be artificially 

 oxygenated, no secretion would occur. 



Unfortunately, I was not aware of more recent physio- 

 logical work on this subject when I made this last sug- 

 gestion. Since then, however, Prof. Halliburton has 

 kindiv directed mv attention to the papers of Bainbridge 

 and Beddard {Biochemical Journal, i., 1906) and Cullis 

 (Jour. Physiol., xxxiv., 1906), in which the reverse result 

 has been obtained ; that is to say, according to these later 

 experiments, a secretion can be obtained from the "renal- 

 portal " circulation provided that the tubule epithelium is 

 maintained in a healthy condition by means of a sufficient 

 supply of oxygen, and that powerful diuretics like urea 

 and phloridzin are employed. This result at first sight 

 appears to be contradictory of my previous conclusion and 

 ronfirmatorv of the generally accepted " portal " theory 

 of the renal cardinal meshwork, but it is the object of 

 these remarks to show that such is, after all, not neces- 

 sarily the case. 



In the first place, these recent experiments have clearly 

 shown that the " renal-portal " circulation will not yield 

 the slightest secretion in the absence of powerful diuretics ; 

 in other words, the result obtained by Bainbridge, Beddard, 

 and Cullis is at best an abnormal one. Under more normal 

 conditions, i.e. in the absence of diuretics, with a healthy 

 tubule epithelium and with the " renal-portal system " 

 alone working, no secretion whatever occurs. 



Secondly, the very fact that when the venous blood con- 

 tained in' the renal' cardinal meshwork alone "supplies" 

 the kidney, the tubule epithelium degenerates, proves that 

 in the normal living animal this blood is not in contact 

 with the tubules, i.e. does not take part in the formation 

 of the blood-plexus surrounding the tubules, since, as the 

 experiments prove, these latter require the oxygenated 

 blood derived from the renal arteries in order to live and 

 much more to secrete. 



Thirdly, it must be remembered that in the experiments 

 of Bainbridge, Beddard, and Cullis, the elimination of the 



