March 7, 1895] 



NATURE 



449 



The following statistics will show the relation of these iron ' 

 lines to the Fraunhofer lines In the region F — D over which 

 the spot work extends. In the table, " terrestrial lines" means 

 lines which have been photographically recorded by myself or 

 my assistants in the spectrum of some metal or another during 

 the past tweniy-fnur years ; " unknown " means a line not so 

 far traced by me in any metal with the exception of Cerium. 

 This exception is necessitated by the fact that the spectrum of 

 that metal contains practically as many lines as appear in the 

 solar spectrum. The wave length map of Rowland's second 

 scries has been taken as a standard. 



, 1880 

 /1200 



82 



84 



86 



88 



90 



92 



94 



96 



NUtVIBER 



TIMES 



WIDENED I 



In the present communication I confine myself to submitting 

 provisional curves based upon a preliminary inquiry into the 

 number of times the lines of both categories have been 

 observed to be widened in spots. S'>me slight correc'ions will, 

 doulitless, he ultimately required when a few uncertainties con- 

 nected with some of the earlier observations, made before Row- 

 land's maps were available, have been cleared up. The 

 highest points of the curves represent the maximum frequency 

 of iron lines in one case and of unknown lines in the other. 



The period embraced by the observations practically enables 

 us to study what has taken place at two successive sun-spot 

 minima and two maxima. It will be 

 seen that the phenomena which followed 

 the minimum of 1S79 have been 

 exactly reproduced after the minimum 

 of 1S90. At the minima the iron 

 lines are prominent among the most 

 widened lines ; at the maxima we only 

 find lines about which nothing is 

 known. Since the discussion indicates 

 that the iron lines involved, which ulti- 

 mately disappear, ate almost invari- 

 ably those seen most prominent in the 

 spark, the view put forward in my paper 

 of 1886 that the change observed is 

 due to the dissociation of iron in the 

 spots as a sun-spot maximum is ap- 

 proached, is corroborated, and, so far, 

 I have heard of no other simple and 

 sufficient explanation. 



It will be noted that the maxima 

 and minima of solar temperature thus 

 revealed to us, If my hypothesis be con- 

 firmed, lag behind the spot maxima 

 and minima. This may explain the 

 lag observed in those meteorological 

 conditions, the secular changes in 

 which have been held by Balfour 

 Stewart, Broun, Meldrum, Blanford, 

 Chambers, and others, to prove that 

 the distuibances and changes in our 

 own atmosphere are affected by those 

 taking place in the atmosphere of 

 the sun. 



1800 82 



84 



86 



88 



90 



92 



94 



96 



VARIATION IN ANIMALS 

 AND PLANTS.' 



'T'lIE importance of variation as a 

 factor in organic evolution is not 

 seriously dispuied ; but, if one may 

 judge from the expres-ions ci,n'amed 

 in recent essays, naturalists aie not 

 agreed as to the manner in which 

 variation among individuals is asso- 

 ciated wiih specific modification. 



The view originally put forward 

 by Darwin and Wallace is that 

 specific modilication is at least 

 generally a gradual process, result- 

 ing from "the accumulation of innumerable slight varia- 

 tions, each good for the original possessor" ("Origin cf 

 Species," chap. xv.). This view rests on the assumpiion that 

 each of those small differences which are to be observed among 

 a g'oup of individuals belonging to the same species has 

 generally some effect upon the chance of life. " Can we doubt 

 (remembering that many more Individuals are born than can 

 possibly survive) that individuals having any advantage, how- 

 ever slight, over others, would have tlie lest chance of sur- 

 viving and of procreating their kind?" ("Origin of Species," 

 chap. iv. ). 



Of late years, another view has received support from various 

 writers. An examination of any series of animals of the same 

 species preserved in a museum sliows in most cases a large 

 majority of specimens which are superficially alike : those 

 individual diftercnces, upon which stress is laid by Darwin and 

 by Wallace, are often so slight as to escape attention tjnless 

 minute comparison is made between individual and individual. 



■ A paper read at the Royal Society on Fcl>ru.-iry aS, by Piof. W. V. R. 

 Weldon, F.R.S. 



NO. 1323, VOL. 51] 



