412 



NATURE 



[December 12, igi: 



for convenience is called zero. If, therefore, a 

 certain area of this is insulated, it can only remain 

 at the potential of the remainder so long as it 

 receives or loses no charge. If it was losing a 

 charge before it was insulated, it can only be 

 kept at zero potential after insulating by supply- 

 ing it with the charge lost. In 1906 C. T. R. 

 Wilson designed an instrument by means of which 

 an insulated plate could be kept at zero potential 

 while exposed to the atmosphere, and the charge 

 which had to be supplied to do this could be 

 measured. The result proved an actual loss of 

 negative electricity. The amount of this loss was 

 found to be equal to that which can be calculated 

 from a knowledge of the potential gradient and 

 the conductivity of the air. 



Realising that the plate in Wilson's instrument 

 did not exactly represent a piece of the ground 

 and that measurements at odd times could always 

 be objected to, a method was developed in Simla 

 by which a continuous record could be obtained 

 of the charge necessary to keep at zero potential 

 a large area — 17 square metres — which was to 

 all intents and purposes a part of the surface of 

 the ground. This instrument was in use for 

 nearly a month, and registered a continuous loss 

 of negative electricity. These experiments indi- 

 cate clearly that during fine weather negative 

 electricity actually passes from the earth into the 

 air. This disposes of the possibility of the lost 

 charge being renewed uniformly over the whole 

 earth by such processes as the fall of charged 

 dust, friction of the air on the earth's surface, 

 or the absorption of ions from the air. The loss 

 over the whole earth is equivalent to a constant 

 current of more than looo amperes. As this loss 

 takes place from all regions of the earth, subject to 

 normal or fine weather conditions, it would appear 

 that the return current can only exist in regions 

 of disturbed weather, and it is known that in such 

 regions the potential gradient is often reversed 

 and the rain charged. 



.\ reversed field certainly causes a flow of nega- 

 tive electricity into the earth, but as the time during 

 which the field is reversed in any one place is 

 only a very small fraction of the time duriner which 

 it is normal, the flow of electricity would have to 

 be enormous if the loss were made good in this 

 way. Such a large flow could not possibly escape 

 detection, and no one has seriously put forward 

 this as a solution of the problem. 



There is still the possibility that the electricity 

 comes to the earth in the disturbed area as a 

 negative charge on the rain. For many years this 

 was the most favoured theory for the supply of 

 the negative electricity, but in iqoS-q measure- 

 ments were made in Simla which showed that 

 there, at least, the rain carried down more positive 

 than negative electricity. Since then many 

 measurements have been made on the elec- 

 tricity of rain, and now we have before us 

 the results of observations made in Porto 

 Rico, Simla, Vienna, Potsdam, Puy-en-Velay 

 and Dublin. In everv one of these cases 

 the Simla result is confirmed, and there can be 

 NO. 2250, VOL. 90] 



no doubt now that in all kinds of rain, from the 

 intense rain of thunderstorms to the drizzle of a 

 depression, more positive than negative electricity 

 is brought to the earth. Thus rain, instead of 

 solving our problem, has made it more ditlicult. 



It has been suggested that the charge may be 

 returned in the lightning of thunderstorms. Prof. 

 Schuster has discussed this point in his recent 

 book, "The Progress of Physics" (p. 150), and 

 comes to the conclusion : " It does not seem to 

 me, judging by present information, that lightning 

 discharges from cloud to earth can play an im- 

 portant part in increasing or diminishing the 

 charge of the earth," and there are other reasons, 

 not mentioned by Prof. Schuster, for coming to 

 the same conclusion. 



We have now discussed the conditions in dis- 

 turbed areas and have not found the return current, 

 for neither the reversed field, the precipitation, nor 

 the lightning provides it. Thus the science of 

 atmospheric electricity has come to a deadlock, 

 and there is at present no indications of a way 

 out.i We may sum up the position in the follow- 

 ing statement. A flow of negative electricity takes 

 place from the surface of the whole globe into 

 the atmosphere above it, and this necessitates a 

 return current of more than 1000 amperes; yet not 

 the slightest indication of any such current has so 

 far been found, and no satisfactory explanation 

 for its absence has been given. 



George C. Simpson. 



PROF. FRIEDMANN'S TREATMENT OF 

 TUBERCULOSIS. 



THE announcement of the successful application 

 of any new method of treating tuberculosis 

 must always arouse intense interest and create new 

 hope among those who are suffering from, or 

 waging war against, this disease. For the latest 

 of these, dexised by Prof. Friedmann, of Berlin, 

 it appears to be claimed that it acts not only cura- 

 tively in cases where tuberculosis has already com- 

 menced, but prophylactically where there exists a 

 danger of infection to those not already tuber- 

 culous. A large number of cases have been treated 

 in Berlin and Vienna, and it is said that where 

 the disease is not far advanced it is cut short, and 

 that in children as yet unaft'ected the tissues and 

 organs have been protected against the invading 

 tubercle bacillus. This therapeutic agent appears 

 to be some form or preparation of a non-virulent 

 tubercle bacillus or some bacillus nearly allied 

 which has been deprived of its toxic constituents 

 or products. 



In view of the outcome of the experiments made 

 by the Royal Commission on Tuberculosis on the 

 immunisation of animals by the use of injections 

 of living tubercle bacilli, it is almost to be desired 

 that the vaccme is of the nature of a prepared 

 proteid and does not contain any living bacilli, 

 however modified. Judging from the accounts we 



1 Prof. Ebert has proposed an explanation, but against it fatal objections 

 have been raised. Those interested might consult the series of articles 

 which appeared in the Physikalisclu Zeilschri/t between March, 1904, and 

 December, 1905. 



