NA rURE 



[December i6, 1909 



of Trade, which was very favourably received. The 

 popularity of the present manual and its imme- 

 diate precursors has been greatly increased by its 

 adoption by the Board of Trade as a text-book in con- 

 nection with the examination of masters and mates 

 in the mercantile marine service. It has been pre- 

 pared under the superintendence of Commander 

 Hepworth, marine superintendent of the Meteorologi- 

 cal Ofifice, formerly a keen observer of meteorological 

 phenomena in various oceans. Several new charts 

 have been constructed from the materials in the pos- 

 .session of the meteorological committee, and show, 

 inter alia, the mean isobars for the middle months of 

 each quarter, and the pressure and prevailing winds 

 for January and July over the globe, with an in- 

 teresting discussion of the leading features exhibited. 

 Cows, Cow-houses, and Milk. By G. Mayall. Pp. 



xi + io2. (London: Baillifere, Tindall and Cox, 



1909.) Price 2S. 6d. net. 

 The above title covers a lot of ground for a small 

 book of about a hundred pages. Naturally, we expect 

 to find the information much condensed; thus, in the 

 chapter on breeds, little more than a page is given to 

 the premier race: Shorthorns. -Again, in feeding 

 cattle and in the variations of milk, we are told, in 

 the one case, a fair ratio is i to 6 or 7, and, in another 

 place, 5 lb. to " lb. of good oats is said " to improve 

 fat yield and milk taste." We should have preferred 

 to have seen the starch equivalent and protein in the 

 ration explained in a different way. Breeders, like 

 other people, cannot be expected to agree on all points, 

 and we should wish to have our heifers served long 

 before "at the end of their second year." 



The illustrations are very good, and misprints in the 

 reading matter appear to be very few. One may be 

 pointed out on p. 56, concerning the average per cent, 

 of fat in cream, which may be anything from 25 per 

 cent, upwards ; also, on p. 63, 40° C. should read 

 40° F. Of the hygiene and veterinary sections we 

 have nothing but unstinted praise. Everyone inter- 

 ested in this important subject should read " Checking 

 the Spread of Disease." The book can be commended 

 to the improving landowner, the land agent, the dairy 

 farmer, and tlie short-course student, who requires 

 much information in a limited time. 

 The Oxford Geographies. (Oxford : Clarendon Press, 



1909.) The Elementary Geography. By F. D. 



Herbertson. Vol. II., '/n and About our Islands. 



Pp. 112. Price IS.. Vol. IV., Asia. Pp. 128. Price 



is.6d. Vol. VII. The British Isles. Pp. vi + 192. 



Price is. gd. 

 Cambridge County Geographies. Gloucestershire. 



By Herbert .A. Evans. Pp. X+1S5. Westmorland. 



By Dr. J. E. Marr, F.R.S. Pp. 1x4-151. (Cam- 

 bridge : University Press, 1909.) Price is. 6d. 



each. 

 The characteristics of the series of elementary books 

 of geography to which the new volumes under notice 

 belong have been described already in these columns 

 (vol. Ix.x.xii., p. 125). In the three new parts of Mrs. 

 Herbertson 's *' Elementary Geography," it is satis- 

 factory to find the same simplicity of language, cor- 

 rectnessof information, and abundance of well-chosen 

 illustrations which served to make the earlier volumes 

 admirably adapted to the requirements of junior 

 classes. 



Both Mr. Evans and Dr. Marr have entered into 

 the spirit of the scheme of the Cambridge County Geo- 

 graphies, and their accounts of Gloucestershire and 

 Westmorland respectively maintain the high standard 

 of the series. Geography is given the same wide 

 interpretation, and the books include a description of 

 the architecture, natural history, and geology of the 

 counties dealt with. 



NO. 2094, "^'OL. 82] 



LETTERS TO THE EDITOR. 



[Tlie Editor docs not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of NATURii. 

 No notice is taken of anonymous communications.] 



The Atomic Weight of the Radium Emanation. • 



In a paper by Mr. A. J. Berry and myself read before 

 the Royal Society on December 9, on the thermal con- 

 ductivities of gases at very low pressures, we showed that 

 for the heavier monatomic gases, neon and argon, the 

 experimental conductivity agreed (as well as could be ex- 

 pected from the present state of the measurements) with 

 that calculated from the kinetic theory from the number 

 of impacts of the molecules per sq. cm. per second and 

 the molecular heat of the gas, assuming perfect interchange) 

 of energy on impact. 



This suggests a possible means of obtaining experimental 

 evidence on the much-debated question of the atomic weight 

 of the radium emanation. If a moderate fraction of a 

 gram of radium were available the infinitesimal quantity 

 of the emanation would not be an insuperable difficulty, 

 for at the sufficient pressure of 004 mm. the emanation 

 from this quantity would occupy the sufficient volume of 

 2-2 c.c. The pressure of the emanation could be deduced 

 from existing data by means of 7-ray measurements; but 

 also, with hardly any elaboration of the apparatus, an 

 accurate determination of the volume of the emanation 

 could be obtained. For it may be remarked, without in 

 any way reflecting upon the numerous and careful experi- 

 ments that have been done on this volume since its first 

 determination six years ago by Sir William Ramsay and 

 myself, the purification of the emanation by ordinary 

 methods appears at the best to be imperfect ; whereas to 

 an operator experienced in the use of the calcium method, 

 worked out in this laboratory, no difficulty is to be 

 anticipated. 



On the view discussed in our paper, the thermal con- 

 ductivities of the heavier monatomic gases should be 

 inversely proportional to the square root of their atomic 

 weights, so that the atomic weight of the radium emana- 

 tion could be compared with those of the heavier argon 

 gases by a novel method. Frederick Soddy. 



Physical Chemistry Laboratory, University of 

 Glasgow. 



Alkali syenites in Ayrshire. 



It is now well known ihat a g-oup of basic alkalic 

 rocks of approximately late Carboniferous or early Permian 

 age occurs in central Scotland. Dr. Teall first remarked 

 the teschenitic affinities of some of these rocks in his 

 " British Petrography " (1888). During the recent work of 

 the Geological Survey in central Scotland, many occur- 

 rences of teschenite, essexite, and theralite have been 

 recognised by Mr. Bailey and Dr. Flett. In several locali- 

 ties the teschenites pass into picrites of the Inchcolm type. 

 .Although the general facies of this group is quite basic, and 

 locally ultra-basic, the presence of acid veins in some of 

 the teschenite intrusions has encouraged the hope that a 

 more acidic phase might be discovered in some of the 

 lesser known intrusive masses of central Scotland, hitherto 

 indiscriminately lumped together as "dolerites." 



This hope has been realised by the discovery of a large 

 mass of alkali-syenite at Howford Bridge, near Mauchline. 

 This mass, which is intrusive into the Permian lavas of 

 the central Ayrshire basin, is finely dissected by the river 

 -Ayr. It is_ composed mainly of a peculiar medium-grained 

 rock, consisting of thoroughly idiomorpbic felspars, prin- 

 cipally anorthoclase, with subordinate albite and ortho- 

 clase, a little nepheline, numerous small crystals of ^girine, 

 brown and bluish-green soda-amphiboles fbarkevicite and 

 arfvedsonite) in mutual intergrowth, and ilmenite altering 

 to leucoxene. The well-shaped crystals of felspars are 

 loosely crowded together, and the angular spaces between 

 them filled with abundant fresh analcite, which encloses 

 the a^glrine and soda-amphibole, as though these had been 

 pushed aside by the crystallisation of the felspars in a 

 thoroughly liquid magma. This rock passes downward 



