528 



NA TURE 



\_April 3, 1884 



i38i." M. Krupp does not give any details of the expe- 

 riments on which he professes to have founded his tables, 

 or ackno%vledge any kind of assistance from any other 

 author. He remarks that for a long time the resistance' 

 of the air was supposed to vary as ?'-, then to depend 

 upon two powers of v, and afterwards to vary as v'^ or 2i\ 

 Experiments have shown that these so-called laws of 

 resistance are not good for all velocities. " Cette experi- 

 ence devait le faire paraitre utile de trouver une nouvelle 

 method pour Ic calcul des vitesses restantes " (p. 16). 

 And again, " Un tel tableau pour differences de vitesse 

 de 10 cm. a eti5 etabli par I'usine Krupp au commence- 

 ment de I'annce iSSo" (p. iS). 



M, Krupp's tables are precisely the same as those that 

 have been used in England since 1871, except only that 

 French replace English measures, and that a small reduc- 

 tion of the English coefficients of resistance has been 

 made throughout. Taking one of Krupp's examples (last 

 page) 1 1/6/79, where d — 355 mm. = I3'977 inches ; w = 

 525 kilos. = 1 1 57 '43 lbs. ; commencing velocity 490 m.s. 

 = 1607 '64 f.s. ; remaining velocity 415 m.s. = I36r57fs., 

 at distance 2384 m. = 782 1 '6 ft. ; weight of i cubic metre 

 of air = l'20o kilos., M. Krupp finds from his table 

 4ir8ms. for the remaining velocity instead of 415 m.s. 

 given by his experiment. My table gives a remaining 

 velocity of 4057 m.s. But supposing we reduce the co- 

 efficients of resistance in the proportion 99^9 : 109 o given 

 by the experiments made with the 5-inch gun (solid shot), 

 then we obtain 4l2'o m.s. for the required remaining 

 velocity, which is nearly the same as 41 18 m.s. obtained 

 by the use of Krupp's table. Again, taking the experi- 

 ment 6/8/79 with a projectile 400 mm. in diameter, com- 

 mencing with a velocity 5334 m.s., M. Krupp finds a 

 remaining velocity of 447 'o m.s. by the use of his table, 

 while I obtain 440^4 m.s. and 443'8 m.s. is given as the 

 result of experiment. But if I reduce all my coefficients 

 as before in the ratio 99^9 : 1090, then my table gives 

 447 '4 m s. as the remaining velocity, which agrees with 

 M. Krupp's calculations. Hence it appears that M. Krupp 

 claims by these tables that his guns of 1880, on the 

 average^ give a degree of steadiness about equal to that 

 given by the best of the four English experimental guns 

 used in 1S67-68. I have not much confidence in the 

 accuracy of velocities measured at a distance of near one 

 mile and a half from the gun by an instrument not speci- 

 fied, but I have used these data as a means of indicating to 

 what extent the tables give different results. As a test of 

 the tables I should much prefer a careful determination 

 of the commencing velocity of the shot, and the time of 

 flight to some known distant point, where all the times 

 were measured by a si/igle instrument. 



For further information I beg leave to refer M. Krupp 

 to (i) "Tables of Remaining Velocity, Time of Flight 

 and Energy of various Projectiles, &c.," 1S71 ; (2) to the 

 Proceedings of the Royal Artillery Institution, Woolwich, 

 September l87l,p. 382, &c. ; (3)//'., April 1872, p. i, &c. ; 

 (4) //'., December 1877, p. 250, &c. ; (5) "Treatise on the 

 Motion of Projectiles, Sic," 1873 ; (6) "Principles of Gun- 

 nery," by Major Sladen, R.A., 1879; (7) " Handbook for 

 Field Service" (R. A.), 1878; (8) "The Construction of Ord- 

 nance, &c.," p. 359, &.C., 1877 ; (9) " Reports on Experi- 

 ments, &c., 84/B/2853," 1879; (10) "Final Report on 

 Experiments, &c., S4/I5/2909," 18S0 ; and (l i ) and (12) 

 " Manual of Gunnery for H.M. Fleet," 1880. And since 

 that date my " General Tables " have been reprinted in 

 four different books. 



Since the above was written, I have noticed that the 

 introducer of the Navy Estmiates, 1884, remarked: — 

 " The old hreccli-loader had been found to be of no more 

 use than a muzzle-loader, and the Government had 

 adopted a gu7i twice as long as the old form of breech- 

 loader." 1 always understood that the profitable use of 

 the new slow-burning powder required a long barrel, and 

 th It the bret cS lo.ndmg arrangement was introduced be- 



cause it permitted the use of a longer barrel on shipboard 

 than could be employed with muzzle-loading. 



March 22 FRANCIS Bashforth 



THIRD NOTE ON THE ELECTRICAL RESIST- 

 ANCE OF THE HUMAN BODY 



T N two previous communications last year, I showed that 

 ■'• the amount of this important basis of rational elec- 

 trotherapeutics had been enormously overstated. Since 

 then I find it given in the new edition of Rosenthal's 

 " Elektricitiitslehre," published in the current year, as 

 about 5000 ohms, and, to my surprise, so competent an 

 observer as my friend Prof. Dolbear, in Lockwood's 

 " Handbook of Electric Telegraphy," states it vaguely 

 as from 6000 to 10,000 ohms. On the other hand, Count 

 Du Moncel, in his paper on the conductivity of imperfect 

 conductors in the Annates tie Clieinie et de Pliysiqiie, 

 vol. .X., 1877, approaches more nearly to the real value in 

 stating it from wrist to wrist to vary from 350 to 220 

 kilometres. This is probably the Swiss unit given in 

 Clark and Sabine's tables as equal to 10-42 ohms or there- 

 abouts. Both Rosenthal and Du Moncel furnish internal 

 evidence that their excessive estimates were due to im- 

 perfect contact through the skin : for the former speaks 

 of using fifty chromic acid elements of two volts E.M.F. 

 each ; whereas the current from this large battery, with 

 proper contact, would be utterly unbearable to the patient, 

 if not dangerous. The highest current 1 have seen em- 

 ployed was from twenty-two of these cells through less 

 than 2000 ohms resistance. It was done against my 

 advice, and produced a large carbuncular boil at the nape 

 of the neck, where the negative pole was applied. I have 

 since then completely modified my method of making the 

 skin contacts, and no similar accident has occurred. 



Even with a far smaller current, namely, that of eight 

 Daniell cells and small platinum electrodes, of which the 

 size is accurately given, namely, 4j by 3 cm. (roughly, the 

 length of two shillings side by side, and the breadth of a 

 florin), Du Moncel produced a similar though much more 

 serious accident. The current was passed at intervals for 

 an hour and a half from wrist to wrist, the patient being 

 a lady, and afterwards for shorter periods in the opposite 

 direction. "On withdrawing the electrodes," says the 

 writer, " to my great astonishment I found, on the parts 

 of the wrists where my electrodes had been applied, very 

 pronounced scars resembling burns produced by an acid 

 or a caustic. These scars, to the number of three at 

 the negative pole, were large and deep. At the positive 

 pole they were very small, and thirty-two in number. 

 During the first two days after the experiment no inflam- 

 mation supervened, but on the third day it began about 

 the negative scars, and it was necessary to have recourse 

 to poultices, which were kept up for a month ; even then 

 the sloughs were not detached." It is satisfactory to find 

 that no permanent harm was done ; but it is evident that 

 the excessive resistance recorded, amounting at times 

 to 3500 ohms, was mainly due to this cause. It is perhaps 

 not to be wondered at that the scientific Count should 

 have relinquished this branch of his investigation. 



With hands soaked in strong brine, and then enveloped 

 in a thickness of flannel wetted with the same solution, 

 bandaged surgically over this with a spiral strip of lead at 

 least 30 cm. long and 5 cm. broad, no local accident has 

 ever occurred to me, nor has any local pain been men- 

 tioned. But with ten bichromate cells in good order the 

 shock felt at making and breaking circuit has often been 

 considerable. Indeed my tall and athletic clinical clerk, 

 Mr. Sh,ickel, who kindly consented to act as a resistance, 

 noticed that, when being tested from foot tohand (in his case 

 a length of 7 feet) with 1027 ohms resistance, the opposite 

 side of the body was jerked at these instants. In all 

 recent experiments I have never exceeded this E.M.F., 



