390 



NA TURE 



[February 27, 1902 



The examples are numerous, and admit of geometrical 

 interpretation ; many of them illustrate the theory of 

 tangential transformations, which, happily, receives a 

 {;ood deal of attention. The articles on existence- 

 theorems appear to be sound, so far as they go, and are 

 unusually readable. Altogether, Dr. Liebmann's book 

 may be recommended as a useful introduction to the 

 modern treatment of the vast subject with which he 

 deals. M. 



The Theory of Equations : with an Introduction to the 

 Theory of Binary Al^ebraie Forxis. By W. S. Burn- 

 side, M.A., D.Sc, and A. W. Panton, M.A., D.Sc. 

 Fourth edition. 2 vols. Pp. xiv -f 286 and xii -I- 292. 

 (Dublin : Hodges, Figgis and Co., Ltd. ; London : 

 Longmans, Green and Co., 1899, 1901.) 

 In this new edition of a well-known and popular treatise 

 the principal change is the addition of a chapter on the 

 theory of substitutions and groups. Following the 

 methods of Serret, Jordan and Netto, the authors give 

 just so much of the elementary theory of substitution- 

 groups as to enable them to prove the fundamental 

 property of the Galoisian resolvent of an equation, and 

 to demonstrate that the general equation of any degree 

 higher than the fourth cannot be solved by an algebraic 

 formula. It is strange that no reference is given to the 

 work of Kronecker and others on equations which do 

 admit of algebraic solution. 



LETTERS TO THE EDITOR. 



[The Edilor does not hold hiniseif responsible for opinions ex- 

 pressed by /lis correspondents. Neither can tie undertal^e 

 to ■return, or to io> respond with the writers of, rejeclei 

 manuscripts intended /or this or any ot/ier part of NATURE. 

 No notice is taien of anonymous communications.'^ 



Note on Electric Charging and Discharging at a 



Distance. 

 A NUMBER of experiments, which I began in 188S, continued 

 in 1S94 and again in 1896, have been waiting for publication 

 until the completion of certain others that I have been hoping 

 to find time to carry out. As, however, the results are some- 

 what akin to those on the discharge of insulated bodies that 

 are of great interest at the present time, it may be worth while 

 not longer to delay publishing a preliminary note on a few of 

 them. 



The interest of the experiments lies partly in the fact that 

 I was not merely able to disc/tarf;e an electroscope by means 

 of various bodies, hot and cold, placed within distances from 

 it varying between I cm. and 300 cm. , but that I was also able 

 to charge the electroscope by the same means. The special 

 interest, however, arises from cold bodies, viz. cotton wool 

 dipped in ether, methylated spirit, or dilute sulphuric acid, 

 being different, so far as I am aware, from any that have hitherto 

 been employed for discharging or charging an electroscope at a 

 distance. 



A gold-leaf electroscope was employed, its outer case properly 

 screened with strips of tinfoil, and the knob replaced with a 

 metal pot to increase its capacity. A charge sufficient to make 

 the leaves diverge by rather more than a right angle was generally 

 given, so as to render the collapse easy to see. In every case 

 the sign of the charge was tested before it was noted. 



I, — Discharging an Electroscope at Shoit Distances by means 

 of a Candle Flame. — With an insulated candle flame at 15 cm. 

 distance, the leaves collapsed in forty seconds, whether they 

 were charged positively or negatively. At 40 cm. between the 

 two, the positive charge leaked away more slowly than the 

 negative. With 42 cm. distance, the leakage was very slow for 

 both, and at 48 cm. there was none. 



When the candle was earthed, by having a wire sticking into 

 the wick, the discharge was quicker than when it was insu- 

 lated, but not if the wire dipped into the melted wax. The 

 flame of a match had no less power, and an electric arc no more 

 power, than an uninsulated candle flame placed at the same 

 distance. 



II. — Discharging an Electroscope at Long Distances by means 

 of an Insulated Candle. — The candle and the electroscope were 

 next placed 150 cm. apart and a negative charge given to the 



NO. 1687, VOL. 65] 



electroscope. Result — no leakage. A glass rod was then 

 rubbed, brought up to the candle on the side remote from the 

 electroscope, and then withdrawn. When this had been done 

 several times, the leaves began to collapse, and collapsed in 

 jerks, each time the rod was excited, brought near the candle 

 and withdrawn. The collapse appeared to take place at the 

 withdrawal of the rod. The same experiment was performed 

 with distances varying up to 200 cm. between the candle and 

 electroscope, and the numbers of withdrawals and re-excitations 

 of the glass rod that were needed before the leaves began to 

 collapse were noted. It varied from i, with a distance of 125 

 cm. between candle and electroscope, to 14, with a distance of 

 203 cm. Thus the number of excitations increased very rapidly 

 with the distance. The same results were obtained by charging 

 the electroscope positively and bringing rubbed sealing-wax up 

 to the candle. The further the distance of the two apart, the 

 longer was it before the leaves began to collapse and the 

 slower was the collapse when it began. 



III. — Charging an Electroscope at Lmtg Distances by means 

 of an Insulated Candle. — All the experiments in II. were 

 repeated, but the electroscope and the candle were now 

 charged with the same sign. The number of withdrawals 

 before the leaves began to move was much the same as before, 

 but now the leaves diverged more widely, whether both electro- 

 scope and candle were charged positively or negatively. The 

 electroscope was then left uncharged, and the charge rod was 

 brought up to the candle as before. The leaves then diverged, 

 and were found to have a charge of the same sign as that of the 

 rod. Thus a charged electroscope placed at a distance up to 

 200 cm. from an insulated candle can be discharged by 

 repeatedly bringing a charge of the opposite sign near the 

 candle, on the side remote from the electroscope, and, similarly, 

 an uncharged electroscope can be charged with a candle and 

 rod placed at distances up to 200 cm. from the electroscope. 



IV. — The same E.xperiments with an Earthed Candle Flame. 

 — None of the results in IIL are obtained if the candle is 

 earthed. 



V. — Disc/iarging an Electroscope by means of a Red Hot 

 Platinum Wire. — I., II., III. and IV. were repeated with the 

 candle replaced by a platinum wire kept red hot by a current 

 from two Grove's celh, which were placed on a cake of sealing- 

 wax standing on four cubes of paraffm wax when the cells were 

 required to be insulated. The results were practically the same 

 as with the candle flame, except that the platinum wire, when 

 earthed, discharged a negatively charged electroscope, but not 

 one positively charged. Also when it was insulated, it dis- 

 charged the electroscope at as great a distance, in one case, as 

 300 cm. from it. 



Since writing the preceding, I find that some experiments on 

 discharging, and discharging by means of hot bodies placed at 

 s/iort distances from the electroscope, were described by Prof. 

 Worthington at the meeting of the British Association in 1889. 



\\. — To Restore to Platinum Wire the Power to Discharge 

 when it has lost it by being kept IV/iilc Hot for many /touts. — 

 Prof Schuster first observed, I believe, that glowing platinum 

 wire ceased to discharge electrified bodies near it after it had 

 been kept white hot for some ;time. He attributed its dis- 

 charging power to occluded gases and the loss to these having 

 all been expelled. To see if the power could be restored to the 

 wire by placing any substance on it, I first put a drop of oil on 

 some wire that had lost its power, but with no eff'ect. A grain 

 of sugar was equally ineffectual, &c., hut either salt or common 

 washing soda was, I found, instantly efficacious. It seems 

 possible, therefore, that it is some trace of a salt of sodium or 

 other metal on an ordinary platinum wire that either enables, 

 or assists, the hot wire to discharge, and that the while heat 

 chemically cleans this off. I intend, however, to make further 

 experiments on this point. 



\ll.— Charging and Disc/iarging an Electroscope by' means of 

 Cotton Wool dipped in Et/ier, Methylated Spirit, or Dilute 

 Sulphuric Acid— the [w/io/e Insulated.— II., III. arid IV. were 

 next tried, when the candle flame was repKiced with an insu- 

 lated saucer of cotton wool, saturated in turns with ether, 

 methylated spirit and dilute sulphuric acid placed at a distance 

 from the electroscope. Each was found to act just as well as 

 the candle flame and in the same way. None would act when 

 earthed, and carbon dust— dry— was quite ineffectual in both 

 cases. 



Many other experiments were tried, but the precedmg are 

 sufficient to show the nature of the phenomena observed. 



Hertha Avrto.n. 



