460 RECORD OF SCIENCE FOR 1887 AND 1888. 



galena, aud magnetite. Of more general physical character may be 

 mentioned the work of Hustings^ on the double refraction of calcite ; 

 remarkable as of a higher grade of accuracy than any experiments of 

 the same kind before made, and which prove the law of Huyghens to 

 be true to less than one part in five hundred thousand. In other words, 

 it is concluded that there is no known method by which an error in it, 

 if it is not absolutely true, can be discovered. Btickstrom- has contrib- 

 uted a paper on the thermo electricity of crystals. An excellent discus- 

 sion of the molecular structure of crystals has been given by Groth, in 

 his address before the Munich Academy. A paper read by J, W. Judd^ 

 before the Mineralogical Society of Great Britain is also an interesting 

 discussion of the development of a lamellar structure in quartz crystals 

 by mechanical means. Abstracts of a number of other papers of 1887- 

 '88 referring more or less closely to mineral physics are given in Groth's 

 Zeitschrift, vol. xv, p. 298 et seq. 



CHEMICAL MINERALOGY. 



Riggs has investigated anew the composition of tourmaline,'' and with 

 improved methods has made a series of analyses, twenty in all, of the 

 widely different varieties from typical localities. The following ratio is 

 established : Si : B : R' : O = 1 : £. : 4; : 5 and the formula R9BO,2Si04 

 where W is the univalent equivalent of the bases with the oxygen-excess 

 incorporated in an A1=0 group. If an O— H group is assumed the for- 

 mula is written, lvioBO.,2Si04. The typical kinds are then 



Lithia tom-iiKilini' l-2SiO> 3B.,0:, 4HiO. BAIjO:,. 2(Na-,Li).20. 



Iron toHimaline I'iSiO,. r5B..0.,. 4H2O3. 7A1,0,. 4Fe0.Niij0. 



Magnesia tonrni:tlinc..I2.SiO> 38,0;;. 4Hj0. ^Al^O;,. AjSMgO.f Na:0. 



Wiilfing" has made the analyses of Riggs the basis of a series of cal- 

 culations designed to throw light upon the composition. He concludes 

 that the various varieties can be regarded as isomorphous mixtures in 

 different ])roportions of the molecules 



Si,,BfiAl,6Na,H80,, and SiuBnzVl,„Mg,,H6063. 



Clarke has added some analyses- to those previously published of 

 different kinds of mica, including a muscovite from North Carolina, and 

 a number of iron micas from different points. The same author has 

 studied the nickel ores of Oregon," which are similar to those of New 

 Caledonia in composition. He concludes that the parent mineral was 

 a nickel-bearing olivine. Whitfield '* contributes a series of analyses of 

 some borates, colemanite, ulexite, ludwigite,axinite, etc.jUsingrecentim- 



'Aiuer. Jonr. Soi., 1888, vol. xx.w, 60. -^Miu. petr. Mitth., 1888, vol. X, 161. 



- (EtVersigt. k. Vet. Akad. Forhandl., t^Amer. Jouru. Sci., vol. xxxiv, 133. 



No. 8, 1888. ' Ibid, vol. xxxx, 483. 



■' Miu. Mag., 1888, vol. viii, 1. »Amer. Jonr. Sci., 1887, vol. xxxiv, p. 281. 

 ^ Auier. .Tonrn. Sci., 1888, vol. XXXV, 3.'). • 



