February 9, 191 1] 



NATURE 



47, 



Not a single grain during all these years was given except 

 10 my hospital and private patients actually suffering from 

 malaria. 



Dr. Bentley thinks it a " ridiculous assumption " that 

 the high death rates of 1900 and 1901 would have re- 

 mained unchecked but for the measures recorded. If he 

 will do me the honour of reading my forthcoming book, 

 he will find it proved (as I venture to claim beyond dis- 

 pute) that in many places in the neighbourhood of Klang, 

 so long as the Anopheline factor remains undisturbed, 

 these high death^-ates do, alas ! without any " absurd 

 fiction," continue. In view of the large increase of 

 population, we are justified in assuming that, but for the 

 measures taken, malaria would have claimed many more 

 than four hundred victims during each of the years under 

 review ; and Dr. Bentley will find that the two cases of 

 anti-malarial works, the reports of which have incurred 

 his criticism, have been paralleled strikingly in numerous 

 instances. 



It is commonly assumed that to rid even small tropical 

 towns of malaria by anti-malarial operations presents in- 

 surmountable difficulties, and that to attempt such a 

 campaign over extensive rural areas w-ould be tilting at 

 windmills. It can be shown, however, that in the 

 Federated Malay States planters have, quite unconsciously, 

 been carrying out great anti-malarial works over far 

 greater areas than Klang and Port Swettenham, for the 

 benefit of much larger populations, at only a small frac- 

 tion of the exp>ense, and with complete success. Indeed, 

 one cannot help suspecting that great anti-malarial works 

 are constantly being carried to a successful conclusion by 

 those whose last idea would be that they were carrying 

 out great sanitary works ; and in view of what has 

 already been achieved it would be rash to deny that the 

 future may have in store for us the final expulsion of 

 malaria from the whole of what is, even to-day, one of 

 the most malarious portions of the tropics. 



Malcolm Watson. 



Klang, Federated Malay States, December 27, 19 10. 



Studies of Magnetic Distutbacces. 



In the number of Natlre for August ii, 1910, Dr. 

 L. A. Bauer published some results of investigations of 

 magnetic disturbances, forming an abstract of papers pub- 

 lished in Terrestrial Magnetism, xv., Nos. i and 2. 



In these papers Dr. Bauer treats a number of problems 

 of the greatest interest for the study of terrestrial mag- 

 netism ; but in my opinion there are certain points of a 

 fundamental nature which it would be w^^ll to take up 

 for discussion, partly because certain of his results differ 

 ■considerably from those of other investigators in this field. 



Dr. Bauer treats the " positive equatorial storms " of 

 May 8, 1902, and January 26, 1903, and concludes from 

 a mathematical analysis "that for both disturbances the 

 -\stenis of disturbance forces which it would be necessary 

 :o superpose upon the earth's own magnetic field were 

 Diecisely of the same character as the earth's. In other 

 words, were we to assume electric currents as constituting 

 the disturbance systems, then, as in the case of the earth's 

 field, the currents would have to circulate from east to 

 ■west if they are positive ones and in the contrary direc- 

 tion — from west to east — if they are negative or such as 

 would be produced by moving negative charges. Further- 

 more, for both disturbances the electric currents would 

 Tiave to circulate chiefly in the regions above the earth " 

 <Nature, loc. cit., p. 192). 



I am not quite sure of what is meant by the expression, 

 that the disturbance field is precisely of the same character 

 as the earth's own field. For a real similarity, which 

 would allow conclusions to a similarity in origin of the 

 two phenomena, we should have provided the following 

 relation 



P = feT (l) 



■where P is a vector representing the perturbing force at 

 a certain place, T is the total force of the earth's per- 

 manent magnetic field at the same place, and fc is a 

 constant. The relation (i), however, is not even approxi- 

 mately fulfilled for any of the principal groups of disturb- 

 ances treated by Birkeland in his work, " The Norwegian 

 Aurora Polaris Expedition, IQ02-1903," not even for the 

 NO. 2154, VOL. 85] 



equatorial storms considered in Dr. Bauer's paper, so 

 that the similarity assumed by Dr. Bauer cannot mean 

 that relation (.i) is fulfilled. 



Then when Dr. Bauer, from the similarity between the 

 earth's own field and the field of the positive polar storms, 

 concludes that the disturbance current systems must circu- 

 late round the earth in the same direction as that which 

 may be supposed to produce the permanent field of the 

 earth, this conclusion is not justified without further 

 proof, for the two similar fields show great differences. 

 I While the forces P and T have the same direction near 

 the equator, this is no longer the case nearer the poles, 

 where their vertical components have opposite directions. 



It seems also difficult to understand how the direction 

 found by Dr. Bauer can be brought into harmony with 

 his statement that the greatest part of the current is to 

 be found above the surface of the earth. For suppose 

 that an electric current — circulating around the earth and 

 above its surface — shall produce the observed perturbing 

 force directed towards the north, it follows from .Ampere's 

 rule that the current must pass from west to east, or in 

 the direction opposite to that found by Dr. Bauer. So 

 long as we regard external systems as forming the primary 

 cause of disturbances, this result must hold even if we 

 take into account the magnetic permeability of the earth 

 and the effect of induced currents. 



Dr. Bauer states that the disturbance systems probably 

 always can be supposed to originate from one internal and 

 one external current system, and for the equatorial storms 

 he has given the mathematical method for separating the 

 two systems. 



The separation was carried out for the perturbation of 

 May 8, 1902, and " the surprising result revealed itself 

 that the internal currents went in the same direction as 

 the external ones, the latter being about three times the 

 strength of the former." 



Now two systems of this kind, keeping on simul- 

 taneously, must in some way be physically connected ; but 

 it seems rather difficult to see how this connection could 

 be produced, for, as Dr. Bauer himself rightly remarks, 

 the internal currents cannot be induced currents. Thus it 

 seems that merely simple physical considerations will 

 make the result very improbable, and besides, I think that 

 objections can be made to the way in which it is 

 deduced. 



I am not going into details regarding the validity of 

 the mathematical method, but I am merely going to show 

 by an example that the method used by Dr. Bauer cannot 

 be trustworthy. 



The equations for the internal systems (see Terr. Mag.y 

 XV., No. I, p. 26) are simply expressing the forces on the 

 surface of a sphere uniformly magnetised along a certain 

 diameter. Suppose, now, that in a plane, perpendicular 

 to this diameter and passing through the centre of the 

 sphere, there was a circular current concentric with the 

 sphere and with a radius large compared with that of 

 Ihe sphere. The magnetic field of the current in the space 

 occupied by the sphere would be nearly uniform, and if 

 the sphere was made of a homogeneous material it would 

 be uniformly magnetised. In other words, the equations 

 which should express a field due to an internal system 

 will in this case express a field actually caused by an 

 external one. The system of equations, however, which 

 according to Dr. Bauer should express the field due to an 

 external system, will not even approximately be able to 

 express an external system of the kind here supposed. I 

 think this will be sufficient to show that the result of the 

 separation will require further proof. 



I should also like to say a few words regarding the 

 direction of the circular current of negative corpuscles 

 which may be formed round the earth in the plane of the 

 magnetic equator. These currents play an impcM-tant part 

 in the kathode ray theory of Prof. Birkeland. and it is of 

 importance that no misunderstanding should exist on this 

 point. 



Dr. Bauer arrives at the conclusion that the direction 

 of motion of the negative corpuscles of such a current is 

 from east to west. I have not from his short note been 

 able to follow his argument, but a simple consideration 

 will show that the corpuscles will encircle the earth in a 

 direction opposite to that found by Dr. Bauer. 



Suppose a negative corpuscle is moving in the plane of 



