April 23, 1896] 



NATURE 



5<^3 



rate of leak is almost independent of the potential 

 difference. Thus in chlorine we found that the rate of 

 leak was practically the same when the potential 

 difference was 278 volts as when it was ten. The rela- 

 tion between the rate of leak and the potential difference 

 thus exhibits the same general features as that between 

 the magnetisation of a piece of soft iron and the magnetis- 

 ing force. 



This result seems to throw light on the manner in which 

 the electricity passes through the illuminated gas, and 

 may perhaps be extended to conduction through ordinary 

 electrolytes. 



M. Stoletow has observed a somewhat similar relation 

 between the potential difference and the rate of leak 

 from a negatively electrified surface illuminated by ultra- 

 violet light. 



Mr. McClelland and I also investigated the connection 

 between the rate of leak and the potential difference in 

 the case of solid dielectrics, such as paraffin and sulphur 

 exposed to the Rontgen rays. We found that this obeyed 

 Ohm's law up to the highest potential difference (278 

 volts) used in our experiments, so that the potential 

 difference required to '' saturate " solid delectrics is evi- 

 dently very much greater than for gases. The polarisa- 

 tion is also much greater for paraffin and sulphur than 

 for gases, and it can be locked up, as it were, in the 

 dielectrics for any length of time by screening them from 

 the rays J. J. THOMSON. 



THE EXPERT WITNESS. 



■\17E are rejoiced to see the daily press at last calling 

 * * attention to the need of reform in the present 

 system of expert witnesses, indicating that public opinion 

 is coming round to the view which we have advocated for 

 the past twenty-five years. The fact that scientific men, 

 some of them even of high standing, can be procured to 

 sustain the most contradictory views is, we have no 

 hesitation in saying, hurtful to the interests of science, 

 and tends to degrade science in the opinion of the public. 



An easy way to secure perfectly unbiassed opinion is 

 to insist that a scientific expert should not be called by a 

 particular side in a case, but should be nominated by the 

 Judge. We have urged the expansion of this system from 

 the Admiralty Court, in which it is constantly employed, 

 and within the past i^^^ days our opmion has been 

 echoed by the daily press. 



Commenting upon the judgments in two actions brought 

 by the Incandescent Gas Light Company against rival 

 companies for infringement of Dr. Welsbach's patent, 

 the Times says : — 



" One reflection is likely to occur to any who has watched the 

 progress of these cases. The substantial question to be determined 

 was one of chemistry and chemical history. The principle of law 

 to be applied was clear and simple. A cloud of scientific witnesses 

 was in attendance, and men of great eminence, such as Sir Henry 

 Roscoe and Prof. Dewar, were called on both sides. The objec 

 tion to this course is not perhaps verj' serious when the litigants 

 are wealthy companies and the patent is of great value. But it 

 must strike any impartial mind that the length of such inquiries 

 would be curtailed, that the expert would be more in his true 

 place than he often now is, and that there would be fewer exhi- 

 bitions of startling conflicts between the opinions of high 

 scientific authorities, if the Court frequently did what it is not 

 customary to do — namely, took the evidence more into its own 

 hands, nominating one expert, or it may be two, to report for 

 its guidance on some of the matters of controversy. An expert 

 reporting as the delegate of the Court would sometimes express 

 himself very differently from one paid for his evidence, and 

 many cases would occupy as many hours as they now occupy 

 days."' 



The Globe also has something to say in condemnation 

 of the present state of things, and its plain words will not 



NO. 1382, VOL. 53] 



be pleasant reading to men imbued with the true scientific 

 spirit. Referring to the same cases as the Times^ it 

 remarks : — 



" From the conflict of expert testimony, which is almost invari- 

 able in these cases, an idea has grown up that such evidence is 

 not very valuable to the plain man, and the average juryman is 

 much disposed, when he hears the eminent experts contradicting 

 one another, to pay little or no attention to either side. The 

 fact is that our whole system of taking expert evidence is 

 founded on a wrong basis, except in the Admiralty Court, where 

 the Judge has the advantage of professional opinion from persons 

 occupying a quasi-judicial position. The expert who is 

 called in an ordinary case receives a fee which varies accord- 

 ing to his reputation, and also according to the length he is 

 prepared to go in supporting the case of those who call 

 him. Naturally, a plaintiff, whose case depends upon, 

 say, a doubtful point in chemistry will search for an 

 expert witness who takes that view of the question which 

 is most favourable to his- contention, and the defendant 

 on his side, will look for one who does exactly the reverse. 

 Hence there is a continual pressure being exerted upon the 

 expert witness to go further in his evidence (han would be the 

 case if he could be impartial, and testimony becomes bewilder- 

 ingly contradictory. A simple remedy for this state of things 

 would be for the Judge to select the expert himself. There are 

 few departments of science in which he would not know of some 

 recognised authority, and, even if he did not, he could always 

 obtain the information. An expert so chosen would, of course, 

 receive his fees from the suitors, but he would give his evidence 

 as the assessor of the Court instead of as the witness of one 

 litigant, the truth would be much more easily got at, and cases 

 that now take weeks would be settled in a few days." 



As in most matters with which science is concerned, 

 Germany is able to show us the best mode of action. 

 Experts are appointed by the State at the discretion of 

 the Judge ; these may be men not suggested by either of 

 the litigants, or chosen by both of them. 



It has been legal in England for some years for a Judge 

 to select an expert to report to the Court upon a particular 

 matter in dispute, and this practice is occasionally fol- 

 lowed. There is thus little difference between the status 

 of the official English expert and the expert of the 

 Imperial Courts in Germany. All that is needed is the 

 substitution of official experts entirely for those called by 

 the parties concerned. Under such a system, no question 

 of bias could be raised, and science would not be scanda- 

 lised from time to time as it is now by those who are 

 content thus to trade on their scientific reputation, and 

 give rise to such unpleasant insinuations as those in which 

 the Times and Globe are pleased to indulge. 



H. C. LEV INGE. 



BOTANIC science has sustained a loss by the death, 

 in the full vigour of middle life, of H. C. Levinge, 

 of Knock Drin Castle, Mullingar, late Secretary to the 

 Government of Bengal (Public Works). During his 

 Indian career he devoted all the time he could spare 

 from official labour to natural history, and especially to the 

 vascular cryptogams. His collection of Indian ferns was 

 the largest and finest hitherto made ; he had himself 

 explored more particularly Sikkim, Kashmir, the Neil- 

 gherries, and the mountains south therefrom. At the 

 very time when, on retiring home, he was preparing to 

 work on his superb collection, the larger and finer part 

 of it was destroyed in the fire of Whiteley's fire-proof 

 warehouse. Froin this cause, and perhaps from the 

 excellence of the late work of Colonel Beddome on 

 Indian ferns, Mr. Levinge, at Knock Drin Castle, 

 devoted himself chiefly to the Irish flora. He contributed 

 several papers to the Irish Naturalist., and to the Journal 

 of Botany ; and added no less than seventy-seven addi ■ 

 tional species to area vii. of the Cybele Hibernica. Most 

 of these were from West Meath, many from the im- 



