September 22, 1910] 



NATURE 



;75 



cautions tuberculous patients should take, and as soon as 

 this Icnovvledge can be brought to the patient and his 

 friends there will be some chance of getting these pre- 

 cautions adopted. There seems to be little doubt that 

 the National Association for the Prevention of Consumption 

 has the power to help and cooperate with similar organisa- 

 tions already in existence, and that it may even be of 

 assistance to the authorities working with and under the 

 Local Government Board, but what they are best qualified 

 10 undertake is, undoubtedly, that national educational 

 movement to which Mr. John Burns has given his official 

 approval. 



The carrying on of this movement requires funds, large 

 funds, and a special appeal committee has been formed, 

 which, acting under the presidency of the Earl of Derby, 

 is setting about to collect, in the first instance, a sum of 

 5000/. annually to be devoted to this work. That the 

 necessary fund will be obtained can scarcely be doubled, 

 especially as a most elaborate system of collecting small 

 sums has been org.anised ; moreover, those who will be 

 most immediately benefited are already taking a very keen 

 interest in making this scheme a success, and the com- 

 mittee have announced that they have already received 

 ofTers of assistance from working-men's clubs and insti- 

 tutes affiliated to the Institute L'nion, and the Billposters' 

 Association of Great Britain ; whilst the post-office 

 authorities have promised assistance, or have granted 

 facilities which will help to form the nucleus of a fund 

 such as could be obtained in no other way. Further, those 

 endowed with a larger share of this world's goods have 

 manifested an equal willingness to help, but the object is 

 such a good one, the outlet for expenditure is so wide, 

 and the promise of such an enormous return is so great, 

 that if five times the sum asked for be subscribed it may 

 be advantageously spent. The time has come when the 

 annual loss of 50,000 or bo, 000 lives from consumption — a 

 preventable disease — is a blot on our civilisation. When 

 we knew not we could not be blamed for our want of 

 initiative and lack of energy, but now that we fenouf, 

 inaction is criminal. 



RECENT PAPERS OX PETROLOGY. 

 I I NUER this head may be included work on the minerals 

 that build up rocks, since modern petrology depends 

 on the understanding of the causes that have brought 

 certain mineral constituents into association. This is true 

 even of the fragmental rocks, where the correct apprecia- 

 tion of a detiital mineral may lead up to the source and 

 the relative age of the deposit. E.xperimental work on 

 minerals has, moreover, almost always a geological aim, 

 though compounds have a way of arising artificially under 

 conditions that seem improbable in nature. 



Improvements in methods of research will be found in 

 Mr. F. E. Wright's paper on the " Measurement of Extinc- 

 tion .Angles in Thin Section " {.imer. Journ. Sci., vol. 

 .\xvi., p. 349), where the intensity of light for different 

 positions of a crystal-plate between crossed aicols is dealt 

 with mathematically. The methods of observation in 

 general use are critically discussed, and the principle of 

 the twinned selenite plate, introduced by Sommcrfeldt in 

 1907, is further developed by the author in his artificial 

 quartz twin plate (p. 374). Since the eyes of observers 

 differ in regard to their sensitiveness to certain tints, this 

 plate may be made wedge-shaped, so that the most service- 

 able tint may be selected. Mr. Wright also introduces 

 (p. 377) a bi-quartz wedge-plate. A plate of right-handed 

 quartz, cut normal to the optic axis, is fixed side by side 

 with a left-handed one of the same thickness. Above each 

 is set a wedge of quartz of the opposite sign of rotary 

 polarisation, the two wedges tapering in the same direc- 

 tion. Except where the wedge and the plate below it are 

 of the same thickness, the two similar wedges will show 

 colours of similar intensity. If a crystal-plate lies beneath 

 the wedge-plate, and is not in a position of extinction, a 

 difference of intensity appears in the two wedges, and a 

 thickness can be selected that gives, by the rotation pro- 

 duced, the most sensitive effect to meet the case of each 

 experiment. 



Dr. J. W'. Evans (Proc. Geol. .^ssoc., vol. xxi., p. 79) 

 gi\'es a useful paper for students on the systematic examina- 

 NO. 2134, VOL. 84] 



tion of a thin section of a crystal with an ordinary petro- 

 logical microscope, in which his double quartz-wedge, 

 described in 1905, is effectively introduced for determining 

 the relative retardation of the lays in a section of a doubly 

 refracting crystal. 



-Messrs. Allen, White, Wright, and Larsen {.imer. Journ. 

 Set., vol. xxvii., p. i) provide a characteristic synthetic 

 study of diopside and its relations to calcium and mag- 

 nesium metasilicates, in which the minerals produced at 

 various temperatures are subjected to a thorough optical 

 examination. Etch-figures are used to show minute 

 crystallographic changes that result from dissolving one 

 member of the metasilicate series in another, the resulting 

 minerals being shown to be actual solid solutions (p. 39). 

 Some of the substaiices produced are as yet unknown in 

 nature, and a rhombic MgSiO, mineral arises at about 

 '3''5°. which resembles olivine in form, and which is quite 

 distinct from enstatite (p. 30). The stable form of MgSiO, 

 is, curiously enough, that known from meteorites only, and 

 is styled clinoenstatite. 



Messrs. WVight and Larsen also introduce us to new 

 views on quartz (ibid., p. 421). In treating of quartz as 

 a geologic thermometer, they make use of Le Chatelier's 

 observation in 1890 that quartz undergoes a reversible 

 change at about 575°, as indicated by a sudden change in 

 its expansion-coefficients, birefringence, and circular 

 polarisation. Miigge regards the lov/ temperature a-quartz 

 as trapezohedral-tetartohedral, and the high temperature 

 /3-form as probably trapezohedral-hemihedral. " .\t or- 

 dinary temperatures all quartz is o-quartz, but if at any 

 time in its history a particular piece of quartz has passed 

 the inversion point and been heated above 575°, it bears 

 ever afterward marks potentially present which on proper 

 treatment can be made to appear " (p. 425)- Quartz 

 formed on the low temperature side, such as that of veins 

 and geodes, shows trigonal trapezohedra, more regular 

 twinning than the 3-form (as discovered on etching), more 

 frequent intergrowths of right- and left-handed forms, and 

 an absence of the effects of shattering that appear in 

 quartz cooled down from the high-temperature form. The 

 authors verify these points by an examination of quartz 

 from ordinary veins and from pegmatites. 



NL Borisov (1 rav. Soe. imp. dcs. Nat. de St.-P^tersbourg, 

 vol. xl., p. 46) describes quartz in druses from the Govern- 

 inent of Olonetz ; the form is the rhombohedron, with a 

 polar angle reading 85° 4-', so that we have a rare type 

 reseinbling cubes. Mr. R. S. Bassler (Proc. U.S. Nat. 

 .Mus., vol. xxxv., p. 133) traces the reinarkable changes 

 by which fossils in the carboniferous limestone of Ken- 

 tucky have been converted into geodes of chalcedony and 

 quartz, and his photographs alone would claim the atten- 

 tion of petrologists and palaeontologists alike. 



Students of silicates will note the paper by Messrs. 

 Shepherd, Rankin, and Wright (.4mer. Journ. Set., vol. 

 xxviii., p. 293), on the binary systems of alumina with 

 silica, lime, and magnesia, in which andalusite and silli- 

 matrlte receive experimental treatment. .\ very useful 

 statement is included (p. 322) as to the six phases of 

 crystallised silica now known, the a and forms, re- 

 spectively, of quartz, tridymite, and cristobalite. Mr. 

 Larsen [ibid., p. 263) examines the refractive indices and 

 densities of some of his artificially prepared silicates and 

 their glasses. Incidentally, he finds that glasses rich in 

 lime and magnesia cannot be prepared, owing to their 

 strong tendency to produce crystals — a tendency well recog- 

 nised among basic igneous rocks. Messrs. Washington and 

 Wright (ibid., vol. xxix., p. 52) discover, in a felspar from 

 the Mediterranean islet of Linosa, a molecule correspond- 

 ing to soda-anorthite, and look forward (p. 70) to naming 

 the actual Na,AI,Si,0, felspar, when forthcoming, 

 Carnegieite. Since the felspar that they really possess is 

 a new species, and receives the name of Anemousite, it 

 seems quite grasping to look so far ahead, even from the 

 verv open windows of the Carnegie Institution. 



Mr. F. Cornu (Verhandl. k. k. Keiehsanslalt. iqoq, 

 p. 41), in ^a preliminary and slightly polemical demonstra- 

 tion, promises an important work on the importance of 

 '■ Hydrogelen im Mineralreiche " which will need to be 

 considered by all who deal with soils and products of 

 decav. The author claims that our method of heatiitg thin 

 slices in Canada balsam removes the water from essential 



