l82 



NATURE 



[August ii, 1910 



rather different. There still remain, however, a number of 

 •details in which improvements must be effected before the 

 machine can be widely used. In another bulletin a descrip- 

 tion is given of an organism producing acidity in milk which 

 appears to be closely related to B. btilgaricus, the charac- 

 teristic organism of Yogurt, and to be widely distributed. 

 ' Messrs. Hart, McCuUum, and Humphrey continue their 

 work on the functions of the mineral constituents of foods 

 •on metabolism in the animal, and show that the skeletal 

 tissues can, if necessary, make good any deficiency of 

 ■calcium and phosphorus in the ration. A low phosphorus 

 intake was accompanied by a high calcium output in the 

 lurine. 



The use of more exact statistical methods in the investi- 

 gation of agricultural problems has already led to interest- 

 ing results, and is likely to prove of great benefit. Mr. 

 V'igor recently discussed the relation between the reduction 

 in area of wheat in England and the increased yield ; his 

 paper is published in the Journal of the Royal Statistical 

 Society (part iv.). The reduction of the wheat area has 

 been accompanied by a rise of the yield per acre in England 

 as a whole, and improvements of the yield often appear 

 to be greatest in those countries where the proportionate 

 reductions of area have been greatest. Counties of low 

 yields do not, however, appear to have been specially 

 selected for a reduction of area. The yields of the various 

 counties have shown a slight tendency to level up. By 

 applying somewhat similar methods, H. Arctowski has, 

 in Bulletin No. 7 of the American Geographical Society, 

 mapped out the variations in the harvest in the United 

 States during the decade 1891-1900. In general, very bad 

 years in one region of the globe are years of excellent 

 yield in another region, but the centres of compensation 

 are not always found in the same regions nor is the 

 compensation always exact ; otherwise the supply would 

 be constant. 



The Scotch Education Department has issued in con- 

 nection with the Royal Scottish Museum, Edinburgh, two 

 useful guide-books, " An Introduction to Petrography and 

 Guide to the Collections of Rocks," published in 1909, and 

 " A Guide to the Scottish Mineral Collection," published 

 in igio. Both are from the pen of Dr. S. ]. Shand, who 

 is in charge of the geological department of the museum, 

 and both are sold for the modest sum of one penny. The 

 guides have been specially compiled from the point of view 

 of Scottish minerals and rocks, and are written in simple 

 and, so far as possible, untechnical language, so as to 

 appeal to the ordinary visitor unversed in these subjects. 

 A few pages of the rock guide are devoted to a descrip- 

 tion of the collection of rocks of the Christiania district, 

 which has,' owing to Prof. Brogger's exhaustive studies, 

 become classical in the science of petrology. Copious 

 indices add to the usefulness of the books. 



The Tanami goldfield in Central Australia was discovered 

 in the year 1900, but its development has been delayed by 

 the scarcity of water and its situation in a remote part 

 of the continent on the eastern frontier of Westralia. The 

 general geographical and geological conditions of the gold- 

 field are described in a short report by Mr. H. Y. L. 

 Brown, the Government geologist of South Australia. 

 (Government Geologist's Report on the Tanami Gold 

 Country, Northern Territory of South Australia. Pp. 

 12 ; three maps. Adelaide : 1909.) Mr. Brown shows 

 that the oldest rocks of the district belong to a series 

 of slates, quartzites, and schists which, though pne- 

 Cambrian, are stratified sediments. They have been in- 

 vaded by plutonic rocks, including diorite and felsite, and 

 NO. 2128, VOL. 84] 



covered by a series of limestones and dolomites, which he 

 identifies as Lower Cambrian, and by quartzites, sand- 

 stones, and boulder beds, which he regards as probably 

 Permo-carboniferous. There are widespread volcanic 

 rocks, mainly basalts and volcanic ashes, which Mr. Brown 

 assigns to eruptions ranging from Mesozoic to Cainozoic. 

 His description of extinct craters suggests that some of the 

 eruptions are of recent age. The gold occurs in lodes 

 numerous in the pre-Cambrian sediments near the junction 

 with the intrusive diorites, and also in " lode formations " 

 in the igneous rocks. The mines are at present little more 

 than prospecting shafts. The gold in the quartz is coarse, 

 and where it occurs in the altered igneous rocks it is finely 

 diffused. The widespread limestones and basalts produce a 

 rich soil, and if adequate water can be obtained, the dis- 

 trict will Be valuable for pastoral purposes, while Mr. 

 Brown regards the gold discoveries as promising and 

 important. 



In a short article in the PhysikaUsche Zcitschrift for 

 August I, Messrs. R. A. Houstoun and J. Logic direct 

 attention to the fact that aqueous solutions of ferrous 

 ammonium sulphate form a good filter for stopping heat 

 rays. Alum solutions are, it is now known, no better 

 than water in this respect. A glass cell, of inside thick- 

 ness 3 cm., filled with a solution of ferrous ammonium 

 sulphate, transmitted 75 per cent, of the light and 5-1 per 

 cent, of the total radiation from a carbon glow-lamp ; 

 when filled with water it transmitted go per cent, of the 

 light and ii-i per cent, of the total radiation. The light, 

 it should be stated, forms about 3 per cent, of the total 

 radiation. 



The Physiknlisclic Zeilschrift reproduces in its number 

 for July 15 a communication made recently by Dr. F. 

 Ehrenhaft to the Academy of Sciences of Vienna on an 

 ultra-microscopic method of measuring the electric charges 

 carried by small particles. The particles investigated were 

 of the noble metals, and were produced by means of an 

 electric arc between electrodes of the metal concerned. 

 The air containing the particles in suspension was drawn 

 into an ebonite enclosure in front of the objective of a 

 Zeiss ultra-microscope placed with its axis horizontal, and 

 illuminated from the side in the usual way. The enclosure 

 contained the plates of a small condenser the axis of which 

 was adjusted to be vertical. With the condenser un- 

 charged, the time of fall of a particle through a measured 

 distance in the field of view was observed ; the condenser 

 was then charged in such a direction that the particle 

 ascended, and its speed again observed. Finally, the con- 

 denser was short-circuited, and the speed of fall again 

 determined. .Assuming that Stokes's formula for the resist- 

 ance to the motion of a sphere in a viscous fluid holds for 

 the particles investigated, the magnitudes of the electric 

 charges carried by the particles come out smaller than 

 iXio-'° electrostatic units, a conclusion which does not 

 accord with the view so generally held at present that the 

 " atom " of electricity is 4-6x10-'° electrostatic units. 



The " Metzograph Grained Screen " takes the place of 

 the ordinary cross-lined screen in photo-block making, and 

 differs from it in giving an irregular grain and in requiring 

 a shorter exposure. It does not produce its effect by 

 stopping a large proportion of the light, as the cross-lined 

 screen does, but by the lens-like action of the irregularities 

 of its surface. It is produced by obtaining by sublimation 

 a reticulated film on the surface of a glass plate, and then 

 etching with hydrofluoric acid, the film acting as a resist. 

 The screen was invented by Mr. James Wheeler about 

 thirteen years ago, and as the little differences in its 



