94 



NA TURE 



[May 25, 1905 



of King's College. Students will enter Westminster 

 Hospital Medical School as in the past, and will remain 

 Westminster men : they will not become matriculated 

 students of King's College, but they will be taught the 

 earlier subjects of study at that institution. The scheme 

 will come into effect at the commencement of next winter 

 session in October. At the same time, the teaching of 

 the subjects of the final examination is being completely 

 re-organised. It is believed that this commencement of a 

 probably more genera! concentration of the teaching of 

 the preliminary and intermediate subjects of the curriculum 

 cannot but promote the best interests of medical education 

 in London. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, March 9. — "On some Continuous Observ- 

 ations of the Rate of Dissipation of Electric Charges in 

 the Open Air." By Dr. C. Coleridge Farr. Communi- 

 cated by Dr. C. Chree, F.R.S. 



During part of 1902 and 1003 the author resolved to 

 take as many observations of the rates of dissipation of 

 electric charges as possible, and to continue them over 

 the whole day, and, when opportunity offered, over longer 

 periods. 



The observations were made on the Canterbury Plains 

 of New Zealand, about 20 feet above sea-level, and five 

 miles due west from the sea coast. The apparatus used 

 was Elster and Geitel's ' Zerstreiiungsapparat. Corre- 

 sponding observations were made of the direction and in- 

 tensity of the wind (Beaufort), the humidity, and the 

 potential difference between a point about 10 feet above 

 the ground and the earth. This was determined by a 

 Kelvin portable electrometer and a water-dropper. 



The dissipation apparatus was read by a telescope, and 

 at night it was illuminated by a bull's-eye lantern, but 

 only during the actual time of reading. 



The conductivity of the air is very irregular, but on an 

 average negative electricity is dispersed more rapidly than 

 positive. 



y ,■ _ conductivity of air for — ve electric ity 



conductivity of air for -hve electricity 



six ordinary days, embracing several hundreds of observ- 

 ations, gave an average of q = i-i6. 



Yet on several occasions for some hours together during 

 these six days, positive electricity was dissipated the more 

 rapidly. The examples considered apparently indicate that 

 a low value for q is, as might be expected, accompanied 

 with a reversal of sign of the atmospheric charge. On 

 one occasion, however, the potential became — 185 volts 

 with q about unity. 



Again, considering the six days only, as more typical of 

 ordinary conditions than two others to be referred to, there 

 is distinct evidence of a double maximum and minimum 

 value for the conductivity throughout the dav for charges 

 of both signs. 



Of two other days, viz. February i and 2 and December 

 15 and 16, the former exhibits no distinct maxima and 

 mmima, but a strong south-west gale was blowing ; the 

 latter day is incomplete. 



Observations on February i and 2, and on March i 

 and 2, during south-west gales gave a much higher value 

 for the conductivity for both positive and negative charges 

 than usual. Since the wind on these two davs was in the 

 same direction, there is only a slight amount of evidence 

 that the excessive conductivitv is due to the strength rather 

 than to the direction of the wind. 



Two days not yet mentioned, viz. February 18 and 

 March 16, may now be referred to. On the first 'of these a 

 strong gale from the north-west was blowing when the 

 observations were begun. On the latter, at 6.30 a.m 

 It was calm; at 8 a.m. there was a light south-west 

 wmd, and at 9.30 it was blowing stronglv from the north- 

 west _ with a characteristic falling barometer. These 



nor westers " blow over a range of mountains reaching 

 7000 feet, and deposit their moisture on the western slopes 

 though the rain often extends to the eastern side. In 



1 Elster and Gei.el, "Terrestrial Magnelism," vol. iv., p. ^x^cise,. 



NO. 1856, VOL. 72] 



Christchurch they are invariably dry and hot, being of the 

 nature of " Foehn " winds, and have a depressing effect 

 upon most people. 



Though the above days are the only two of the class 

 upon W'hich, so far, the author has taken dissipation 

 observations, yet potential observations indicate that the 

 winds are negatively charged relatively to the earth, which 

 is contrary to the usual condition. On both days the dissi- 

 pation curves show marked peculiarities. The earliest 

 observation, at 11.15 a-ni' on February iS, gave 5 = 0-4, 

 with a negative potential difference between water-dropper 

 and earth of —300 volts at 10.20 a.m., —150 volts at 

 11.40 a.m., and —50 volts at 12.45 P-tri' Corresponding 

 with this rise of potential there is also a marked rise in 

 the value of q. 



On March 16 the whole history is apparent. At 

 7.30 a.m. the wind was light south-west, 9 = 1-3, potential 

 -1-90 volts. At 9.45 a.m., wind north-west, strong, 

 g = o-7, potential —250 volts. At 10.30 a.m., wind north- 

 west, strong, <; = i-i, potential —100 volts approximately. 

 The north-west wind seemed then to have thoroughly 

 established itself. The values of q became less and less, 

 the curves indicating the conductivitv of the air for positive 

 and negative charges diverging rapidly, that for positive 

 reaching a high value, whilst the negative curve reached 

 remarkably low values. Corresponding w-ith the extremely 

 low value for ij the potential reached its greatest negative 

 value, — 1S85 volts. Alter this q increased and the 

 negative potential decreased, until at 4.30 p.m. 5=094, 

 potential —30 volts. 



March 30. — " On a New Type of Electric Furnace with 

 a Re-determination of the Melting Point of Platinum." 

 By Dr. J. A. Marker. Communicated by Dr. R. T. 

 Giazebrook, F.R.S. 



The first part of the paper deals with a description of a 

 new type of electric furnace for the attainment in absence 

 of noxious gases of temperatures between 800° C. and 

 2200° C. The conductor conveying the electric current 

 is a tube of solid electrolytes similar in composition to 

 the filament of a Nernst lamp. .-Xn essential feature is 

 that, for many purposes, the .usefulness and life of a 

 furnace constructed in this way mav be much increased 

 by adopting a " cascade " system of heating. That is, 

 the energy supplied may be divided, so that only sufficient 

 is put through the tubular conductor itself to raise its 

 temperature, say 1000° C. above its surrounding, the 

 surrounding itself beirtg maintained at 1000° C, thus 

 enabling a temperature of 2000" C. to be attained in the 

 tube without straining it unduly. 



The regulation of temperature in small furnaces of this 

 type is so perfectly under control that very well defined 

 melting points may be taken with very small quantities 

 of substance. 



The second half of the paper deals with a re-determin- 

 ation of the melting point of platinum by the thermo- 

 electric method in these furnaces, the highest value found 

 being 1713° C, the lowest 1702° C, and the mean result 

 of the experiments 1710° C.+s° C. 



May II. — "The Effect of Plant Growth and of Manures 

 upon the Soil: the Retention of Bases by the Soil." By 

 A. D. Hall and N. H. J. Miller. Communicated by Prof. 

 H. E. .\rmstrong, F.R.S. 



The investigation deals first with the variations in the 

 amount of calcium carbonate — the only basic substance 

 usually available in soils — in the experimental plots at 

 Rothamsted. In four of the fields which have been un- 

 manured during a long period, the loss of calcium car- 

 bonate amounts to about 1000 lb. per acre per annum. 

 This rate of loss is much increased on some of the manured 

 plots ; the use of ammonium sulphate and chloride, as 

 sources of nitrogen, causes an increased loss of calcium 

 carbonate which is equivalent to the amount required to 

 neutralise the acid of the salts applied. 



When sodium nitrate is used as a manure the rate of 

 removal of calcium carbonate is lower than on the un- 

 manured plots. Farmyard manure has also a similar con- 

 serving effect on the calcium carbonate in the soil. 

 Evidence is also brought forward showing that many soils 

 which are initially very poor in calcium carbonate retain 

 their fertility unimpaired for many years, and even show 



