142 



NATURE 



{Dec. 16, 1880 



is split up be of different degrees of volatility— of different 

 molecular -weight— we may expect that measurements of 

 the displacement of different lines will not all furnish the 

 same results. Mr. Lockyer states that in an observation 

 of a sun-spot on August 31 of this year, when the iron 

 line at X 52oy6 was doubly contorted, indicating an 

 ascending and descendingvelocity of about fifteen miles a 

 second, the two adjacent iron lines at X 52037 and 52or6, 

 visible in the same field of view, were perfectly steady. 

 Observations of this kind are necessarily very difficult, 

 and the communication is made with all reserve ; but it is 

 to be hoped that observers elsewhere will co-operate in at 

 once putting this observation to the test. 



It is difficult to exaggerate the importance of the 

 question to the chemistry of the future, for should it once 

 be proved that the dissociation of the so-called elements 

 is taking place in the sun and still hotter stars, it will 

 be within the power of the physicist with the aid of the 

 telespectroscope to build up a theory of elemental evolu- 

 tion not inferior in interest to the doctrine of organic 

 evolution. For my part, I have no fear of the result, for 

 apart from Sir Benjamin Brodie's hypothesis and apart 

 from spectroscopic evidence, I believe that in the relations 

 of the "elements" to each other when arranged more 

 or less in accordance with the now well-known periodic 

 law of Mendeljeff we have distinct proof of progressive 

 development, but of this I hope to say more on another 

 occasion. 



Sir B. Brodie points out in his lecture that if the sym- 

 bol a"- were assigned to hydrogen, instead of the symbol 

 a, a different symbolic system analogous in its form to 

 the system in vogue amongst chemists would result 

 In the second part of the Calculus he has fully ex- 

 plained his reasons for adopting the hypothesis a, not- 

 withstanding that it leads to conclusions so entirely 

 different from those ordinarily accepted, the chief reason 

 being that this hypothesis satisfies the so-called law of 

 even numbers — the law that the sum of all the units of 

 affinity in a compound is an even number. The recent 

 remarkable discovery — probably one of the most im- 

 portant theoretically ever made by chemists — of the 

 behaviour of the halogens at high temperatures would 

 appear to furnish an opportunity of experimentally ascer- 

 taining whether Sir B. Brodie's hypothesis a is admissible, 

 for this hypothesis would not admit of a simple resolution 

 of the diatomic molecules of chlorine, bromine and 

 iodine into monatomic molecules which has been regarded 

 as the more probable explanation of the results obtained 

 by Victor Meyer and by Meier and Crafts. Two 

 well-established exceptions to the law of even numbers 

 exist, nitric oxide, NO, and nitric peroxide, NO2, but 

 as is well known, Sir B. Brodie has suggested that in 

 these we may not be dealing with homogeneous gases, 

 but that each is constituted of two gases which, taken 

 together, are made up of oxygen and nitrogen, but which 

 separately are not so made up : hypothesis a would lead to 

 similar conclusions regarding the constitution of chlorine, 

 bromine and iodine at high temperatures. 



At present all that is established, however, regarding 

 the halogens is that iodine begins to undergo dissociation 

 at a temperature between 600° and 700°, and that its 

 vapour gradually diminishes in density until at a white 

 heat it attains not far short of half the " normal" value. 



Whatever the nature of the dissociation products, the 

 occuiTence of dissociation must be regarded as placed 

 beyond doubt, for Victor Meyer's results have been in the 

 main confirmed not only by Meier and Crafts, but also 

 by Deville and Troost, who had previously obtained 

 normal results. Bromine does not undergo dissociation 

 so readily as iodine, the ratio of the observed to the 

 theoretical " normal " density being, according to Meier 

 and Crafts, '8 for bromine when it is '66 for iodine. In 

 a recent communication, Victor Meyer has stated that the 

 results of his earlier experiments with chlorine would 

 appear to have been vitiated by some as yet undiscovered 

 source of error; this gas probably is not dissociated except 

 at extremely high temperatures, and it is doubtful whether 

 there is any difference in behaviour between free and 

 nascent chlorine, Henry E. Armstrong 



HANDBOOK OF BOTANY 

 Handbucli der allgemcinen Botanik. Von Prof. Dr. N. 

 J. C. Muller. Zweiter Theil. Allgemeine Morphologie 

 und Entwickelungslehre der Gewiichse. Pp. 4S2, 

 Figs. 277. (Heidelberg, 18S0 : Carl Winter's Universi- 

 tatsbu chhandlung. ) 

 'n~'HlS is the second instalment of a work by a single 

 -L author which is to treat of all the different depart- 

 ments of botanical science. The first volume, which is 

 devoted to the consideration of the Physiology and 

 General Anatomy of Plants, was reviewed in Nature, 

 vol. xxi. p. 589. It is impossible to pass a more favour- 

 able verdict upon this volume than upon its predecessor. 

 It is characterised by the same failing, namely, a want of 

 clearness and definiteness in the statement of important 

 ficts and fundamental principles. The first section of 

 the book is devoted to a discussion of the theory of 

 descent, the origin of species, and the occurrence of 

 varieties and monstrosities, with the object, presumably, 

 of making the reader acquainted with some, at least, of 

 the influences which determine the forms of living 

 organisms. The account of the morphology of plants 

 begins at p. 38, and after ten pages of general considera- 

 tions the subject is actually grappled with. Prof Muller 

 commences with the Thallophytes, though he does not 

 call them so, for his first section on them is headed " Der 

 Algenstamm." It is not easy to understand what he 

 means by the suffix "stamm" ; does he mean to describe 

 the thallus of the Alga as being a " stem," or does he use 

 the word in the sense of " tribe " ? Whichever be the 

 true interpretation, it still remains unexplained why this 

 word should appear as the heading of a section which 

 treats not only of Alga;, but of Fungi as well. The 

 prospectus of the work sets forth that the Classification 

 of Plants is to form the subject of a subsequent volume, 

 and there is therefore some hope that Prof. Midler will 

 there give a classification of the .'Mga: which is more in 

 accordance w^ith facts and with reason than the one 

 which he now follows. It is impossible to imagine on 

 what grounds the Palmelleas, the Protococcae, and the 

 Volvocineae should be united together to form the Order 

 Palmellaceffi, and yet this is done on p. 51 of this work, 

 although the author is evidently aware of the fact that in 

 Volvox reproduction is effected by means of sexually 

 produced oospores, as his account of that plant, a singu- 

 larly inaccurate one be it said, on p. 62 testifies. 



