;oo 



NA TURE 



[September 2, 1909 



those of the cube. The points of intersection we consider 

 as those representing the molecules, inasmuch as any point 

 within tlio limits of the cell may equally well be taken 

 to represent the cell and the molecule, provided the choice 

 is analogously made throughout the structure. 



It has recently been found possible to determine the 

 relative dimensjons of these molecular cells, the distances 

 of separation of the points of the space-lattice, in those 

 cases where we know that the structure is similar, as in 

 isomorphous salts; and the interesting discovery has been 

 made that the " molecular distance ratios," as these space- 

 dimensions are called, are functions of the atomic weights 

 of the interchangeable members of the family of chemical 

 elements constituting the series, just as the crystal angles 

 have been shown to be. 



We are now able, moreover, to take yet one further step, 

 for the chemical molecules are composed of atoms, and it 

 has been indubitably shown that the atoms occupy definite 

 positions in the crystal. For when we replace, say, the 

 alkali metal in a sulphate or selenate by another, we 

 observe a marked alteration in the crystal angles and the 

 molecular distance ratio along a particular direction, this 

 direction being the same whichever metals of the group 

 are interchanged ; whereas if we replace the sulphur by 

 selenium, a similar kind of alteration occurs, but along a 

 totally different direction. Now we know that the atoms 

 are arranged in the chemical molecule in what is known 

 to chemists as their stereometric arrangement, depending 

 on the maximum satisfaction of their chemical affinities. 

 Hence this important experimental fact of the occupation 

 by the atoms of definite positions in the crystal proves, 

 first, the homogeneous similarity of arrangement of the 

 molecules, and, secondly, explains why we have classes or 

 subdivisions within the systems. For it is the arrange- 

 ment of the atoms within the molecule which causes the 

 variations of the degree of symmetry, within the limits 

 prescribed by the system and space-lattice ; in other words, 

 which determines the class. 



Now obviously any one of the atoms in the molecule 

 may be chosen to represent the latter, and the points thus 

 chosen analogously throughout the structure will constitute 

 the molecular space-lattice. Hence the whole structure 

 may be considered as made up of as many interpenetrating 

 similar space-lattices as there are atoms in the molecule. 

 The crystal structure will thus be dependent on two factors, 

 the space-lattice and the scheme of interpenetration of the 

 space-lattices, the former dominating the style of architec- 

 ture, the crystal system, and the latter the vagaries of the 

 style, the crystal class. Sohncke has shown that there are 

 sixty-five such vagaries possible, which he terms regular 

 point systems, and these coincide with sixty-five of the 230 

 possible modes of partitioning space. 



These are the broad, simple facts, now proved up to the 

 hilt, which explain the majority of crystal structures, all, 

 in fact, but a very few, of the more complicated classes 

 of the thirty-two. For the remaining 165 ways of appro- 

 priating space all fall into a very small number of crystal 

 classes. They are of very great interest, however, and 

 involve an entirely new principle, that of " reflective " or 

 " mirror-image " symmetry, enantiomorphism as it is 

 technically termed, and include those crystals which possess 

 the remarkable property of rotating the plane of polarised 

 light. These are the cases the geometrical possibility of 

 which has been accounted for by the simultaneously in- 

 dependent work of Schonflies, von Fedorow, and Barlow, 

 and to which we were experimentally introduced by the 

 discovery of the right- and left-handed varieties of tartaric 

 acid by Pasteur. The latter has since been followed by 

 the revelation of many similar cases of two forms of the 

 same chemical substance, related crystallographically and 

 structurally like a right hand to a left-hand glove, and 

 optically differing by the direction in which they rotate a 

 beam of plane polarised light. 



With their discovery and explanation the elucidation of 

 the seven styles of crystal architecture and their thirty- 

 two subdivisions becomes xm fait (iccoinpU, and although 

 many difTicult problems still confront the crystallographer, 

 problems of vast importance to chemistry, the groundwork 

 is now securely laid, the memorable achievement of the 

 last twenty years. The results, moreover, are in entire 



NO. 2079, VOL. Si] 



accordance with the now well-proved fact that the chemical 

 atom is composed of electronic-corpuscles. For the definite 

 orientation of the atom and its sphere of influence within 

 the molecule and the crystal is thereby accounted for, the 

 motion in the solid state so frequently hitherto attributed 

 to the atom being a myth, such motion relating, in fact, 

 to the corpuscles within the atom. 



SOCIETIES AND ACADEMIES. 



Paris. 

 Academy of Sciences, Auj;ust 23. — M. Bouquet de la 

 Lirye in the chair. — The calculation of the roots of 

 numerical equations : M. Uemeray. Referring to a recent 

 paper by M. de Montesgus on this subject, the author 

 points out that he published a method on the same 

 principle in December, 1898. — Movements from the vertical 

 due to the attraction of the moon and sun, the earth being 

 supposed absolutely rigid : Ch. Lallemand. — .\ poison 

 elaborated by yeast : .'\. Fernbach. It has been recently 

 shown by F. Hayduck that there exists in the yeast cell 

 a substance which is toxic to yeast. The present paper 

 contains some new observations on the same subject. A 

 solution of the toxic substance is shown, not only to be anti- 

 septic to yeast cells, but also to bacteria such as B. coli 

 imd .Staphylococcus, although it has no effect on moulds. 

 The most remarkable property of this substance is that 

 it is volatile under reduced pressure at a temperature not 

 above 40° C. The distillate contains no formaldehyde : 

 fi'ither researches on the nature of this sulistance are in 

 progress. — ^The development of the eggs of Philine aperta 

 exposed to the action of radium : Jan Tur. 



CONTENTS. PAGE 



The Use and Misuse of Drugs 271 



Euclid's Elements in English. By G. B M. ... 271 



Hypnotism and Occultism 272 



Electro-technics By Prof. Gisbert Kapp 273 



Our Book Shelf;— 



Snialian : " Leitfaden der Tierkunde fiir hiihere 

 Lehranstahen " ; Smalian and Bernan : " Natur- 

 wissenschaftliches Unterrichtsvverk fur hohere 



Madchenschulen" 273 



Zimmerniann : " Die Photographie " 274 



" Science in Modern Life" 274 



Johnston: "The Central Nervous System of Verte- 

 brates."— Prof. John G. McKendrick, F.R.S. . 274 

 FiippI : " Vorlesungen iiber technische Mechanik" . 274 

 Letters to the Fditor :— 



Beliefs and Customs of the Australian Aborigines. — 



Prof. J. G. Frazer 275 



A Question of Percentages. — Spencer Pickering, 



F.R.S 27s 



The Planar Arrangement of the Planetary System. — 



Dr. T. J. J. See 275 



The Benham Top.— F. Peake Sexton 275 



Man and Animals. (Illustrated.) By R. L 276 



Styles of the Calendar. By W. T. Lynn .... 277 

 African Entomological Research Committee. By 



F. A. D 27S 



The British Association at Winnipeg 278 



Section B. — Chemistry — Opening Address (Abridged) 

 by Prof. H. E. Armstrong, Ph.D., LL'D., 



F.R.S., President of the Section 279 



Section C. — Geology. — Opening Address by Arthur 

 Smith Woodward, LL.D , F.R.S., V.P.Z.S., 

 Sec. G.S., Keeper of Geology in the British 



Museum, President of the Section ago 



Notes 294 



Our Astronomical Column : — 



Astronomical Occurrences in September 298 



The South Polar Spiit on Mars 298 



Comet igogi (Perrine, 1896 VII.) 298 



The Orbits of Certain Spectroscopic Binaries .... 298 

 The Bolide of April 20 as observed in France .... 298 



Materia Medica among the Zulus 298 



American Invertebrates 299 



The Seven Styles of Crystal Architecture. By Dr. 



A. E. H. Tutiop, F.R.S 299 



Societies and Academies 300 



