47 8 



NATURE 



[February i,l 1911) 



considerations in support of the view that while 



i '"\ vapour has an iomsalion potential of one type 



[1 1 volts, i( may also have'an ionisation potential 

 ol .1 second type oi about 2-5 volts. E. Wilson: The 



uremenl of magnetic susceptibilities of low ordi 1 

 11) An instrument which has been designed foi the 

 measurement ol magnetic susceptibility of low order. 

 Ii depends for its action upon ihi pull exerted by an 

 electromagnet in accordance with the well-known 

 Maxwell expression for the mechanical force exerted 

 upon unit volume of the substance. This mechanical 

 force is balanced against the force of torsion in .1 

 phosphor-bronze strip. (2) The instrumental constant is 

 determined from data obtained direct!) with the instru- 

 ment itself, and l>\ thi employment of substances the 

 susceptibilities of which had been measured by other 

 methods. A modified method of using a ballistic 

 galvanometei has been devised which leads to greater 

 sensitiveness. Rock specimens and other substances 

 have been used, and some interesting results obtained. 

 1 1 is shown that the susceptibility of 13 per cent, 

 manganese alio) is much smaller than is usually sup- 

 posed. 1 ,1 The susceptibility of powdered rock speci- 

 mens has been measured and compared with the solid. 

 A ven fail agreement has been obtained between the 

 two, an.l the method has the advantage that powders 

 ran be rapidly made. (4) The susceptibilities <>f 

 varieties of mica have been measured, and it is shown 

 that in certain cases, in a direction parallel with the 

 lamina-, the susceptibilit) ma\ be more than fifty- 

 fold that obtained in a direction at right angles thereto. 

 (5) A scries of liidit aluminium alloys has been tested, 

 and it has been found that, whereas the susceptibility 

 of commercial aluminium is increased by alloying with 

 copper and manganese, it is diminished by alloying 

 with cobalt. (6) It is shown thai the balance could 

 be used to determine rapidh the relative amounts ol 

 ferrous iron in different specimens of glass. 17) Cer- 

 tain specimens' of tourmaline have been examined 

 The green and dark blue opaque varieties have sus- 

 ceptibilities in the direction of the principal crystallo- 

 graphic axis varying from in to 20 per cent, less than 

 in a direction at right angles thereto. The suscepti- 

 bility of rose-coloured tourmaline is very small in com- 

 parison. (8) The papet concludes with a note on the 

 retentivit) of ruck specimens and its possible influence 

 upon magnetic disturbances in magnetii surve) work. 

 Dr. F. Horton and Ann ('. Davies : An experimental 

 ri termination of the ionisation potential foi electrons 

 in helium. An investigation nf the minimum potential 

 difference through which an electron must fall in order 

 to I" alilt lo ionise an alolll of helium on collision with 

 it has he, 11 made b) methods capable of distinguish- 

 ing between ionisation of the "as and secondary effects 

 due to radiation. It has been found that radiation is 

 produced when electrons having a velocity of 204 volts 

 collide with helium atoms, and that this is not accom- 

 panied 1>\ any ionisation of the gas. It has also been 

 found that ionisation of the helium does not occur 

 until tin '■ elocit) of the elei tt ons is raised to 25-6 volts. 



and that no other tcpe of radiation is produced : I 



this point . 



Linnean Society, Januan 16. Sit David Prain, 



president, in tin (hair. ('apt. A. W. Hill: Horticul- 

 tural work carried out in the military cemeteries in 

 France since 19:6. Reference was also made in the 

 paper to the cemel ries in the Italian and other 

 theatres of war. [I nded to make the ceme- 

 teries, so far as possible, smooth, well-kept grass- 

 lawns, surrounded l>\ lad • . ol thorn, beech, or horn- 

 beam, with groups, avenui oole-hedges of trees, 

 such as Siberian crabs, limes, hornbeams, willows. 

 «tc, and to plant on tin gt 1 bushes, iris, and 



NO. 2572. VOL. I02] 



othet dwai 1 , arpeting-plants. Steps are also bi 



taken, where possible, lo mark the cemeteries when 



' anadian, Australian, New Zealand, Indian, and othei 

 Overseas soldiers lie buried with plants native to thi 

 countries whence the) came to the defence ol 



Empire. Allusion was made to the problem, 

 have to be faced in the matter of soil and sit,-, which 

 often ie,,,i,, successful gardening work verj difficult. 

 Some ol the cemeteries are in verj sand) places, 

 others in chalk, whilst a number are in the fenland 

 of the Belgian border. 



Geological Society, Januan 22. Mr. G. W. Lamplugh, 

 president, in the chair. C. J. (iilbert : The occurn 



Of extensive deposits of hi^h-level sands mill gravels 



resting upon the chalk at Little Heath, near Berk- 

 hamsted. In a pit at l.ittl, Heath Common, , 

 plateau of the Chiltern Hills, the following sei 

 has been developed : Surface soil with bleached flint 

 pebbles from the Reading beds, about 2 ft. in thick- 

 ness; pebbl) cla\ and other Glacial deposits, var; 

 from 2 ft. to 20 ft.; stratified loam) sand, 5 ft. to 

 6 ft.; stratified coarse gravel, 17 ft.; dark clay, with 



black-coaled, unworn flints and small, well-rounded 



pebbles, 6 in.; ami chalk'. Tin- upper Glacial depos 

 is a pebbl) clay. The pebbles are derived from thi 

 Reading b, ,1s. The clay matrix is tough, and the 



tints ol 1 he cla) leave no doubt that it has been d. 1 i\ , ,1 

 from the uppei pari of the Reading beds. The chalk 

 llinls are absent, while the small pebbles of whin 



quartz .and lydite an- seldom met with. On the wesi 

 side of the pit, underlying the pebbly clay, is a dis- 

 turbed mass of Glacial sands and cla) of miscellaneous 

 character. The whole deposit is suggestive of an 

 englacial origin. Beneath the Glacial beds is a 

 stratified deposit of dark reddish-brown, mottled, loami 

 sand. Ihe , ntire deposit is banded with tine I'm,- 1 

 i;i , x , la) . I hei e is almost invariably a break In ; 

 the loamy sands and the gravels. The laminae of the 

 loam) sands do not always follow the contour-line of 

 the beach, but are deposited horizontally. The under- 

 lying gravel deposit consists ,,[ Reading pebbles 

 water-worn flints in equal quantities, with an 01 

 sional pebble of puddingstone from the Reading l» ds. 

 No rocks foreign to the district have been found. I 

 gravel becomes coarser in depth, the lower sei 

 containing a high percentage of large, water-worn 

 flints. The small stones are mostl) Reading pebbles 

 and white quartz. The gravel is homogeneous. 

 Recenl researches indicate that the quartz and 

 pebbles in this district have been derived from the 

 Lower Greensand after the final breach of the Chil- 

 tern scat 11, ill the gaps of which the quartz pebbles 

 are found in such abundance. Reasons are add 

 in support of the contention that the loamy - 

 and gravels are marine deposits laid down in a sh 



s,a. and that the) cannot be of Glacial origin 

 (;. Barrow; Notes on the correlation of the deposits 

 described in Mr. C. 1. Gilbert's paper with the high- 

 level "ravels of the South of England lor the Londi 

 Basin). The mavels belong to deposits of which the 



bai.ler constituents have been derived from two .< 

 one within the chalk escarpment, Ihe other beyond this 

 escarpment, but within that of the Lower Greensand. 

 The constituents of the former arc Reading or other 

 l.iiciv pebbles, and Hint. Pebbles of sarsen 

 not uncommon. The pebbles in the latter area 

 sisi of while quartz .and lydite, all small. " Far- 

 travelled" stones, derived from the Hunter, < 

 boniferous Limestone, Red Chalk, etc., are absent, 

 Outliers of th, finer deposits have been nut with. 



The coai sei caavels 0CCU1 on ihe SOUth Sldl of the 

 Thames up to above 600 ft.; these all rest oil ill. 

 chalk. It has been pointed out that there musl 



