April i, 1909] 



NA TURE 



143 



shows how the commonest ot the popular objections to 

 |»he theorv " rests upon the strange belief that variation 

 'is a rare phenomenon, that favourable variations occur 

 singlv and at long intervals, and, therefore, can have no 

 effect in producing any important change " — an idea which 

 is entirelv at variance'with the actual facts of nature. But 

 while strenuously upholding the sufficiency of the 

 Darwinian explanation of the phenomena of life within its 

 own sphere, he still allows that " neither Darwinism nor 

 any other theory in science or philosophy can give more 

 'than a stcondarv explanation of phenomena." 



A paper bv Sir. E. S. Russell in the Bologna Rivista 

 di Scieitza, entitled " The Evidence for Natural Selec- 

 tion," affords a good illustration of the tone, alternately 

 patronising; and depreciatory, which certain writers think 

 fit to adopt in speaking of the epoch-making work of 

 Darwin, .\fter noticing several of the well-known cases 

 in which the operation of natural selection has been 

 actually demonstrated, and after so far giving his approval 

 as to sav that " the theory of natural selection ... is a 

 very suggestive and valuable one," the author thinks it 

 sufficient "to add that "it is highly probable that natural 

 selection has played a part in evolution," and that it is 

 " the formula of what seems to be a general process in 

 nature, but it is a formula without much content." This 

 is indeed to damn with faint praise. The paper concludes 

 with the cryptic utterance that the theory " must become 

 largelv superseded by the very deepening of our know- 

 ledge of it." 



.■\nother paper in the Rivista by the same writer, on 

 (he " Transmission of .Acquired Characters," contrives to 

 introduce confusion into what is essentially a very simple 

 issue. It is of great importance to know whether a modi- 

 fication induced upon the soma can be transmitted by 

 inheritance : it is of comparatively little importance to 

 know whether soma and germ can be affected in common 

 bv the same external agent, as, for example, by tempera- 

 ture in the case of cold-blooded animals like insects. The 

 two ideas are essentially distinct, and nothing is to be 

 gained by attempting to identify them. 



Darwinism and Darwin loom large in other recent publi- 

 cations. The American Xaturalist, for instance, contains 

 five articles on these subjects, communicated, in the first 

 instance, to a special Darwin memorial session held at 

 Baltimore by the Botanical Society of .America. In these 

 Hrof. W. Trelease discusses Darwin as a naturalist, and 

 his work on cross-pollination in plants ; Prof. F. E. 

 Clements follows with an inquiry into the influence of 

 Darwin in relation to the geography and ecology of plants : 

 while Prof. H. M. Richards winds up with a review of 

 Darwin's on plant-movements. In an independent article, 

 which did not form part of the Baltimore meeting. Prof. 

 E. Linton examines and criticises the " Origin of Species " 

 in the light of recent observations and experiments. 



To the March issue of Himmel mid Erdc Prof. Plate 

 communicates a centenary eulogy on Darwin, originally 

 delivered as a lecture at a festival meeting on Darwinism 

 and evolution, held at the Royal .Agricultary High School, 

 Berlin. The Zoologist for March also has an article, by 

 Prof. \V. C. Mcintosh, of St. .Andrews, on the Darwinian 

 theorv in 1867 and now. This is a reprint, with interpola- 

 tions, of a lecture given by the author in March of the 

 year referred to before the Literary and Antiquarian 

 Societv of Perth. One passage in the original lecture, 

 relating to " the appearance of the various species of 

 Ichthyosaurus in the marine strata of the Chalk period, 

 and the utter blank in reference to any form calculated to 

 throw light on their origin," was incorrect when origin- 

 ally written, and now stands in urgent need of an explana- 

 tory paragraph in view of modern discoveries. 



To the March number of Rassegna Contemporanea 

 (published in Rome) Mr. L'go Giovaitnozzi contributes an 

 article on Darwin's life and works. The article is divided 

 into sections, each dealing with separate periods of the 

 career of the great evolutionist, special attention being 

 directed to the influence of the voyage in the Beagle on 

 his opinions, and to the appearance of the " Origin of 

 Species." In the concluding paragraphs reference is 

 made to Darwin's views on religion. 



" Der gegenwartige Stand der .Abstammungslehre " is 



NO. 2057, '^'oi.. 8ol 



the title of a pamphlet, by Prof. L. Plate, published in 

 Berlin, which purports to be a popular explanation of the 

 doctrine of evolution. After stating that evolution is 

 supported by an overwhelming amount of evidence, and 

 that no other theory is in existence capable of taking its 

 place, and with a reference to its importance to mankind 

 in general and to its bearing on religious belief, the author 

 proceeds to state that, in his opinion, Darwin's selection- 

 theory affords at present the only satisfactory explanation 

 of the mode in which evolution has acted. The mutation- 

 theory of de Vries, he adds, is not new in principle, but 

 merely a restricted form of the selection-theory. Muta- 

 tions are nothing more than pronounced variations, which 

 Darwin called fluctuations or individualities. 



THE ELECTRICAL PROPERTIES OF 

 FLAME.' 



■\X7HEN a flame is brought near to an insulated con- 

 ductor charged with electricity, the charge dis- 

 appears. This is explained by supposing that the gases in 

 the flame arc partially dissociated into ions. A neutral 

 molecule splits up into two ions, one having a negative 

 charge and the other a positive charge. The conductor, if 

 positively charged, attracts the negative ions out of the 

 flame, and their charges when they reach it neutralise its 

 charge. 



When a plate of an insulator, such as ebonite, is placed 

 between the flame and the charged conductor, the ions are 

 still attracted through the plate, but when they reach it 

 they cannot get through, and so remain on its surface. 

 The side of the plate turned towards the flame thus gets 

 a charge of opposite sign to that on the conductor. This 

 shows that the disappearance of the charge in the first case 

 was due to an opposite charge attracted out of the flame, 

 and not to the charge on the conductor escaping into the 

 flame. 



We have a stream of gas rising from the flame, and 

 the ions go up in the stream. The ions of opposite sign 

 attract one another, and when two come together their 

 charges are neutralised, and the two ions are said to have 

 disappeared by re-combination. Thus as we go up in the 

 stream of gas from the flame the number of ions 

 diminishes. If the stream of gas is allowed to pass up a 

 long tube containing along its axis a series of charged 

 electrodes, then the bottom electrode will be discharged 

 first, and then the next one, and so on. The ions are used 

 up in discharging the electrodes, so that the electrodes are 

 discharged in order, beginning with the lowest one. When 

 the lower electrodes have been discharged, the upper ones 

 begin to be discharged, but more slowly, because many of 

 the ions disappear by re-combination before they get far 

 up the tube. .Another effect also comes in ; as the gases 

 cool down the ions do not move so freely through them, 

 and are not so easily attracted by the electrodes. This 

 makes the rate of discharge of the upper electrodes still 

 slower. 



Thus, as we go down towards the flame the number 

 of ions and their mobility rapidly increases, and right 

 inside the flame the number is so large that the flame 

 behaves like a good conductor of electricity. 



When the terminals of an induction coil are connected 

 to two Bunsen burners, sparks can be passed from the tip 

 of one flame to the tip of the other. The temperature of 

 the flame is about 2000° C, so that the density of the 

 gases in it is about one-seventh of their density at the 

 ordinary temperature. The potential difference required to 

 send a spark through the flame is about the same as that 

 required to send a spark through an equal length of air 

 at one-seventh of ordinary atmospheric pressure. It 

 appears, therefore, that the' ions do not make it easier 

 for a spark to pass. This is due to the fact that the 

 current in the spark is greater than the ions can carry, 

 so that the potential difference has to be enough to pro- 

 duce more ions, and so is the same in the flame as in 

 un-ionised air at the same density. 



1 DUcourse r'elivered st the Royal Insliluti 

 by Prof. H. A. Wilson, F.R.S. 



Friday, February 



