July 17, 1884] 



NA TURE 



269 



Fireball 



Reading W. G. Smith's remarks on lightning in last week's 

 Nature (p. 241), recalls to my mind a ball I saw during a 

 storm in the autumn of 1881. The storm had lasted some time, 

 and I sat reading a little back from an open window but facing 

 it. Suddenly it became so dark that I could no longer see. I 

 dropped my book and looked out. A ball of fire was passing 

 through the window into the room. It moved very slowly 

 onwards and downwards towards me, and became almost sta- 

 tionary over my book. At first I thought it rested upon it, but 

 I soon saw it was moving slowly across. Having passed over 

 the book, it turned in the direction of my hand, paused just 

 beneath it, and then sank towards the carpet. At this instant a 

 peal of thunder crashed over the house — it was the very loudest 

 I have ever heard. Annie E. Cocking 



The Elms, Bedford Park, Chiswick, W„ July 14 



Butterflies as Botanists 

 There can be no doubt, as pointed out by Fritz Miiller in 

 your last issue (p. 240), that the habits of insects often indicate 

 affinities in plants. There is doubtless a strong affinity between 

 the Solanaceae and Scrophularineae ; the small oval pollen is 

 almost identical in both. The habits of fungus parasites some- 

 times disclose similar relationships, often more real than is at first 

 apparent ; we have an example of this in the fungus of the potato 

 disease, Peronospora infestans. This parasite is almost peculiar 

 to the Solanacea;, being especially destructive to Solanum, 

 Lycopersicum, and Petunia, but at times it invades the Scrophu- 

 larineae and grows on Anthocersis and Schizanthus. It is not 

 common to find one parasitic fungus attacking the members of 

 two natural orders of plants, but other examples could be given. 



W. G. S. 



A Cannibal Snake 



About eighteen months ago, just previous to my leaving 

 India, at Devalah in the Wynaad, the horsekeepers chased and 

 killed a large cobra, 5 feet 4 inches ; previous to death it was 

 thrown down in front of the door of our house, when, after a good 

 deal of twisting and wavy contortion of the body, it disgorged a 

 small rock snake over 4 feet in length. I had heard of the same 

 thing before in India, so that I do not think cannibalism in 

 snakes is so uncommon as Mr. Evans thinks. 



John Fotheringham 



96, Netherwood Road, West Kensington Park, W., July 12 



FOURTH NOTE ON THE ELECTRICAL 

 RESISTANCE OF THE HUMAN BODY 



TN my communication to NATURE (vol. xxix. p. 528) I 

 *■ described the use of alternating currents and the 

 telephone for the above purpose, and promised to en- 

 deavour to obtain at least an approximate measurement 

 of the E.M.F. developed in the secondary coil of an 

 induction apparatus. This promise I now propose to 

 fulfil. But before proceeding to the special subject of the 

 present note, I should wish to draw attention to a paper 

 which appeared on the 15th of the same month in the 

 Asclepiad, by that able experimentalist Dr. B. W. 

 Richardson. He therein describes not only experiments 

 made with the large induction coil of the Polytechnic, but 

 also others made as early as 1868 in conjunction with the 

 late Mr. Becker, the object of which was to obtain a 

 measure of the resistance of animal structures. 



" The results," says Dr. Richardson, " were not fully 

 satisfactory. They were variable even when the condi- 

 tions under which the experiments were made were 

 entirely the same. This variability we found to be due to 

 decomposition of the animal substance, a decomposition 

 which, however feeble the battery, was sufficient to 

 destroy the precision we desired to obtain." Putting the 

 more recently coined word " polarisation " for decomposi- 

 tion, this expresses exactly the difficulty described by me 

 in my first note. "It was, however, possible," says the 

 doctor, "to make out that blood conducted better than 

 any other structure of the body, and better than water." 



I can now fully corroborate this excellent observation, 

 and perhaps extend its application. 



Physiological and even pathological fluids, such as the 

 serum of dropsy, conduct far better than muscle, bone, 

 and nerve. One instance out of many may serve. In the 

 very first case recorded in my communication to NATURE 

 (vol. xxviii. p. 151) the lowest resistance obtained from foot 

 to foot was 2300 ohms. The patient was then very 

 emaciated, but quite free from dropsy. Towards the end 

 of the case, which after death proved to be one of ulce- 

 rative endocarditis, as I had considered it to be during 

 life, slight but distinct dropsical effusion in the 

 lower extremities set in ; the resistance sank at once to 

 700 ohms, and I had to discontinue my observations 

 from the evident change of electrical conditions. I have 

 since verified the same fact many times, and on it I partly- 

 found the belief, already several times stated, that " the 

 human body, in spite of its large amount of liquid con- 

 stituents, follows a similar thermal law of resistance to 

 that influencing solid conductors, though in a very much 

 higher ratio" (Nature, vol. xxviii. p. 152). 



Dr. Richardson does not seem to have attempted to deter- 

 mine the resistance of the living body, which Du Moncel, in 

 1877, did, and with fairly accurate, if unpleasant, results 

 (Nature, vol. xxix. p. 528). On the discovery, however, in 

 1879, of Prof. Hughes's electric balance, he resumed his ob- 

 servations, this time with an alternating induction current, 

 though he does not himself notice the important change. 

 His results are unfortunately taken in arbitrary units on 

 the graduated scale of 200 parts originally applied to Prof. 

 Hughes's instrument. If there is any way of reducing 

 these fictitious to absolute values, my work will be both 

 lightened and assisted by a proved observer. Blood-clot 

 and serum, white and gray nervous substance, muscle, 

 bone, coagulated albumen, gelatine, and pus were all 

 tested. Some of the results were excellent. For instance, 

 fat, which by one experimenter has been stated to increase 

 the conductivity of the body, is found by Dr. Richardson, 

 as I also have found it, to be an absolute non-conductor. 

 It is almost unnecessary to say that, with so skilled a 

 chemist and physiologist, all proper temperature correc- 

 tions and other similar precautions were most strictly 

 observed. 



I can now proceed to the main topic of my present 

 note. On receipt of the Wurzburg dynamometer it was 

 put in adjustment, and a strenuous effort made to com- 

 pare the indications given with a constant and an alter- 

 nating current, to both of which it is sensitive. But the 

 movable suspended coil made of an ivory core, with a 

 double weight of silk-covered copper wire, hung by a 

 platinum hook, and dipping by its other termination into 

 a vessel of strong sulphuric acid by means of a platinised 

 platinum plate, is very heavy ; takes a long time to get 

 to its full deflection, thus allowing the battery to run 

 down sensibly, and, what is worst of all, has a tendency 

 to " integrate." By this I mean to sum up, by its 

 mechanical inertia, a large number of small, intermittent 

 pulls as given by the reversed current, into an almost 

 identical deflection (less, of course, losses) with that given 

 by the one steady pull of a continuous current. In spite 

 of its beautiful workmanship, it had to be discarded for 

 the present research. Somewhat in despair, I fell back 

 on a similar instrument, shown by me at the Oxford 

 meeting of the Physical Society in June 1882, and there 

 heavily abused. The moving coil in this is made of silk- 

 covered aluminium wire to insure lightness, and the 

 bifilar suspension is made of the silver-gilt wire used for 

 military epaulettes and facings. It is the work of my 

 own poor hands. 



Herr Obach then stated, and the statement was re- 

 peated in your columns, that this material had already 

 been used by Messrs. Siemens for their " dust-re- 

 corders," but had failed by difficulty of making contact. 

 On testing my little toy, I found its resistance had not 



