December iq, 1907] 



NATURE 



16 = 



requires some explanation, and solar radiation suggests 

 itself as a possible cause. Hence we might expect an in- 

 creased conducting power in summer and in day-time as 

 compared with that found during winter and at night. 

 Observation shows, indeed, that the amplitude of the mag- 

 netic variation is considerably greater in summer than 

 in winter, and we know that the needle is at comparative 

 rest dviring the night. The variable conducting power 

 depending on the position of the sun helps us also to over- 

 come a difficulty which at first sight would appear to 

 exclude the possibility of any close connection between the 

 barometric and magnetic variations ; the difficulty is pre- 

 sented by the fact that the change in atmospheric pressure 

 is mainly semi-diurnal, while the greater portion of the 

 magnetic change is diurnal. This may, to some extent, be 

 explained by the mathematical calculation, which shows 

 that the flow of air giving a twenty-four-hourly variation 

 of barometric pressure is more effective in causing a mag- 

 netic variation than the corresponding twelve-hourly 

 variation, but the whole difference cannot be accounted for 

 in this manner. If, however, the conductivity of air is 

 greater during the day than during the night, it may be 

 proved that the twelve-hourly variation of the barometer 

 produces an appreciable periodicity of twenty-four hours in 

 the magnetic change, while there is no sensible increase in 

 the twelve-hourly magnetic change due to the twenty-four- 

 hour! v period of the barometer. 



.\ good test of the proposed theory may be found in a 

 closer examination of the diurnal magnetic changes in the 

 equatorial regions, because, owing to the inclination of 

 the magnetic to the geographical axis, the magnetic 

 changes ought to have a term which does not depend on 

 local time, but on the time of the meridian containing the 

 geographical and magnetic pole. This term has its greatest 

 importance at the equator and at the time of the equinox. 



The value of the conductivity necessary to explain the 

 diurnal variation in the manner indicated depends on the 

 thickness of the layers which carry the currents. If e be 

 the thickness and p the conductivity, and the amplitude 

 of oscillation in the upper layers is assumed to be the 

 same as that deduced from the barometric variation, it is 

 found that pe = 3Xio-'. If e is equal to 300 kilo- 

 metres, the conductivity would have to be as high as 

 10- ", while the observed conductivity of air at the surface 

 of the earth under normal conditions is of the order 

 lo--'; at a height at which the pressure is reduced to one 

 degree per square centimetre, the conductivity would be 

 IQ-'^, assuming the rate of re-combination to be indepen- 

 dent of temperature and the ionising power to be the same. 

 The conclusion is that there must be a powerful ionising 

 agent in the upper layer of the atmosphere. 



November 21. — "The Silver Voltameter." Part I. 

 " On a Comparison of many Forms of Silver Voltameters." 

 By F. E. Smith ; and " k Determination of the Electro- 

 chemical Equivalent of Silver." By F. E. Smith and 

 T. Mather, F.R.S. 



Part II. "The Chemistry of the Silver Voltameter." 

 Bv F. I^. Smith and Dr. T. M. Lowry. Communicated 

 by Dr. R. T. Glazebrook, F.R.S. 



Part I. — Very large voltameters were experimented with. 

 Four of the kathode bowls had a capacity of 500 c.c. each, 

 and in general from 300 c.c. to 400 c.c. of electrolyte were 

 employed. The anodes were coated with electrolytic silver. 

 With a Rayleigh form of voltameter containing an electro- 

 lyte of pure silver nitrate, the mean of fifty-two determina- 

 tions of the electrochemical equivalent of silver was 11 1827 

 milligrams per coulomb, the current being indirectly 

 measured by the Ayrton-Jones balance. With a Richards 's 

 form of voltameter, in which the pot had previously been 

 baked in an electric furnace, the value i.ii828 was 

 obtained, and with a syphon and other modified forms of 

 voltameter the value 11 1827 resulted, pointing to little or 

 no irregularities in the large-size Rayleigh form of volta- 

 meter. Deposits were made when the voltameter was sub- 

 ject to a gaseous pressure of 2-4 cm. of mercury, and were 

 found to be identical with those made at atmospheric 

 pressure. The temperature coefficient is probably nil, and 

 is not greater than i part in 1,000,000 per 1° C. The 

 range in the current intensities was from 0-5 ampi/re to 

 8 amperes. 



NO. 1990, VOL. ']-j'\ 



Part II. — Before a definite value could be assigned to the 

 electrochemical equivalent of silver it was necessary to 

 demonstrate that silver nitrate solutions, giving constant 

 products, could be obtained. This was done by preparing 

 silver nitrate from electrolytic silver, from much used 

 silver nitrate, and from commercial samples of the salt. 

 Attempts to confirm the observations of Novak, Rodger and 

 Watson, Kahle, van Dijk, and others, on the effect of 

 repeated electrolysis of a solution, show that in the form 

 of voltameters described in Part I. there is no increase in 

 the deposit with continued use of a solution which is 

 comparable with that obtained by the observers mentioned. 

 High values for the electrochemical equivalent are obtained 

 if the solution contains oxide, carbonate, chloride, nitrite, 

 or hyponitrite ; low values are caused by acid. Silver 

 chlorate and silver perchlorate appear to give normal 

 deposits, but are more troublesome in use, and have no 

 advantage over the nitrate. 



" On the Normal Weston Cadmium Cell." By F. E. 

 Smith. Communicated by Dr. R. T. Glazebrook, F.R.S. 



In the past many investigators have pointed out that 

 the depolariser may produce variations in the E.M.F. so 

 great as 0002 volt. A mode of manufacture of mercurous 

 sulphate was first sought which could be relied on to give 

 a constant product. The salt was prepared in four ways : — 

 (1) electrolytically ; (2) by chemical precipitation; (3) by 

 re-crystallisation from a solution in strong sulphuric acid ; 

 (4) by the action of fuming sulphuric acid on mercury. 

 The mean E.M.F. of the cells set up with the electrolytic 

 salt is 1-01828 volts; with No. 2 product, 1.01830 volts; 

 (3) gives 1-01832 volts, and (4) 1-01831 volts. The effect of 

 the size of the crystals of the depolariser, to the importance 

 of which attention has been directed by H. v. Steinwehr, 

 was investigated by using crystals varying in size from 

 5 to 30 microns, and it is concluded that no large crystals 

 which are sufficiently soluble to act as an efficient de- 

 polariser can give an E.M.F. appreciably lower than that 

 due to crystals from 5 t.i v' microns long. The recuperative 

 power of the cell \\.i^ h^i.il by short-circuiting for from 

 one minute to fi\' d,i\^. 1 lie temperature coefficient for 

 the range 10° C. to 30^ is given by 



£, = £,7-3-45X10-^- 17)- 0-066 X \0'\t- 17)-. 



Geological Society, November 20. — Sir Archibald Geikie, 

 K.C.B., Sec.R.S., president, in the chair. — Glacial beds of 

 Cambrian age in South .\ustralia : Rev. Walter Howchin. 

 The known extension of these beds is 460 miles from north 

 to south. The greatest width across the strata is about 

 250 miles. The beds form part of a conformable series, 

 with Cambrian fossils in the upper part. The rocks above 

 the glacial beds are purple slates and limestones ; below 

 they are quartzites, clay-slates, and phyllites, passing into 

 basal grits and conglomerates, resting on a pre-Cambrian 

 complex. The beds consist of a ground mass of unstratified 

 indurated mudstone, carrying boulders up to 11 feet in 

 diameter. The thickness of the glacial series has been 

 proved up to tjoo feet. The commonest rock-type among 

 the boulders is a close-grained quartzite. The discovery of 

 ice-scratched boulders has indicated the origin of the beds. 

 The striaj are often as distinct as those in a Pleistocene 

 Boulder-clay. Eighty definitely glaciated boulders have been 

 secured, and other erratics too large for removal noted. 

 Under pressure and movement in their bed some boulders 

 exhibit abrasion, but this produces features not to be con- 

 founded with glaciation. In the movement due to pressure, 

 which induced cleavage, some stones have become distorted, 

 and many show pseudo-striation on exposed surfaces. The 

 lines, however, are of equal size and depth, and parallel to 

 each other over wide surfaces, while the glacial stria; are 

 patchy in their occurrence, of varying intensity, and 

 divergent in direction. Mr. H. P. Woodward's suggestion, 

 that the " Boulder-clay " had its origin from " floating 

 ice," Is considered most in accordance with facts. — .\ 

 formation known as " glacial beds of Cambrian age " in 

 South Australia : H. Basedow and J. D. Ilitfe. Eight 

 miles south of .Adelaide an exposure of the conglomerate 

 is bounded to the east by alternating quartzitic and 

 argillaceous bands of rock, comprising the central and 

 western portions of a fan-fold, partly cut off by a fault. 

 Further evidence of stress in this margin is given. On 



