June i6. 1910] 



NATURE 



477 



is paper gives further determinations of the ratio of 

 ium to radio-active matter in minerals, chiefly those 

 urring in Archaean rocks. Very large relative quanti- 

 i of helium are found, in one instance (a sphene from 

 nfrew Co., Ontario) indicating an antiquity of at least 

 . million years, even if no helium has escaped. The 

 que case of beryl, which, as shown in a former paper, 

 itains much helium with hardly any radio-active matter, 

 discussed. An explanation, suggested by Dr. Boltwood, 

 put forward. It is supposed that beryl, in crystallising, 

 ; separated from the parent magma one of the longer- 

 ^ products of the uranium or thorium series, such, for 

 imple, as radium, ionium, or radio-thorium, without the 

 •ent element. This product would decay, leaving no 

 ce of its presence except the helium generated. Reasons 

 ! given for believing that nothing of this kind has 

 ppened in the cases relied on for measuring time. — 



T. Lattey : The effect of small traces of moisture on 

 velocities of ions generated by Rontgen rays in air. 

 me experiments of Prof. J. S. Townsend (Proc. Roy. 

 c, vol. Ixxxi., A, 1908, 464) on lateral diffusion of a 

 rrow stream of ions moving in an electric field led to 

 ! conclusion that negative ions are much smaller in per- 

 :tlv dry air than in air containing a small quantity of 

 )islure. It was consequently to be expected that com- 

 !te removal of water vapour would cause an increase in 

 » velocity with which negative ions move under the 

 luence of an electric field of force. At his suggestion an 

 /estigation of the velocities of ions in air at low pressures 

 is undertaken, and it was found that, while the complete 

 noval of water vapour had only a small effect on the 

 locities of positive ions, yet the same cause increased 

 velocities of negative ions by a factor rising to as 

 jch as thirty for some of the forces that were used, and 

 is factor appeared to be much larger for larger forces, 

 le velocities of positive ions are known to vary directly 

 th the potential gradient (X) and inversely with the 

 assure (/>) of the gas in which they are travelling ; in 

 her words, 7;/)/X is a constant where v is the velocity, 

 'tween 14 and 29 mm. pressure the following values of 

 /X were obtained: — dry air, 7)/)/X= 1121 ;. moist air, 

 '/X = 78o. In the case of negative ions it is known that 

 hen air is moist 'J is not a linear function of X'/), but 

 at v/>/X increases slightly as X//) increases. The 

 locity is, however, a function of X//), and is independent 



actual values of either X or />. In dry air it was found 



at while v is still a function of X/^, yet the rate of 



-e of V with increase of X//) is considerably more 



han in moist air. This is illustrated by the follow- 



^ Mble :— 



.- when pressure remains constant at 14-3 mm. and 

 irce varies from 056 volt per centimetre to 1-43 volts 

 rf centimetre, velocity increases from 107 centimetres per 

 icond to about 4000 centimetres per second. When the 

 as is slightly moist the corresponding velocities would be 

 oout 32 centimetres per second and 90 centimetres per 

 1. Thus in air containing about 11-5 per cent, (by 

 re) of water vapour the velocities observed were : — 



fmm.) X// = oVq o'lo 



t8o »o ?9 



19-3 ^3 92 



Mean 816 9r7 



" .\. O. Rankine : The variation with temperature of 



-cosities of the gases of the argon group. The ratio 



..iO viscosity at the temperature of steam to that at 



tmospheric temperature has been determined for each of 



KT* 

 le five gases. Taking Sutherland's equation t/ = ^ , 



he values of C have been calculated, and are shown in 

 he following table. C is least in the case of neon ; in 

 act, this is the lowest value yet recorded for any gas. 



NO. 2120, VOL. 83] 



This suggests that neon is the most nearly perfect ga& 

 known. A further interesting point is that C is, m the- 

 cases of argon, krypton, and xenon, proportional to the- 

 critical temperature : — 



He Xe A Kr X 



C 70 56 142 1S8 252 



Tc — [63] I5V6 2105 288 



Tr/C ... — [I 12] i-io 1-12 1-14 

 The critical temperatures of helium and neon are not 

 definitelv known, but it is certain that Tc for helium is- 

 much too low to conform with the above rule. With 

 regard to neon, however, Tc is known to be less than 68 

 absolute, and this does not exclude the value 63° absolute 

 calculated bv means of this rule. It has also been noticed 

 that, with the exception of hydrogen, the same rule holds- 

 good for all other gases the data for which are available. 

 —Dr. W. G. Dufllold : The effect of pressure upon arc 

 spectra. Part ii. No. 4.— Gold.— Prof. B. Hopkinson : 

 Radiation in a gaseous explosion. The pressures produced 

 bv the e.xplosion of a mixture of coal-gas and air in a 

 vessel plated with silver on the inside have been recorded, 

 first with the walls highly polished, and second when the^ 

 walls are blackened. The mixture contained 15 per cent, 

 coal-gas, and was at atmospheric pressure and temperature 

 before firing. The maximum pressure reached in the- 

 explosion was about no lb. per square inch above atmo- 

 sphere, corresponding to a temperature of about 2200° C. 

 It was found that when the walls were polished the maxi- 

 mum pressure was about 3 per cent, higher, and the rate 

 of cooling for the first half-second about 35 per cent, less, 

 than when the walls were blackened. The state of polish- 

 of the walls had a great effect on the rate of cooling, 

 differences hardlv appreciable to the eye making a marked" 

 difference in the'rate of fall of pressure. The heat received 

 by polished and blackened surfaces, respectively, was deter- 

 mined bv means of a bolometer of silver strip fixed to the 

 walls, the remainder of which was black. The change of 

 resistance of this strip during explosion and cooling was 

 recorded bv means of a reflecting galvanometer on a 

 moving film simultaneously with the pressure. From the- 

 rise of temperature of the strip and its capacity- for heat 

 the heat-flow into it could be deduced. It was found that 

 when the strip was polished the heat received during the 

 first quarter of a second after firing was three-fourths of 

 that received by blackened strip in the same period, the 

 pressure record's being the same. Relative rates of heat 

 loss to completely blackened and completely polished walls 

 deduced from pressure records, during 02 5 second, varied" 

 from 06 to 07. Direct measurement of radiation from the 

 gas was made by means of a recording bolometer placed" 

 outside the vessel, and exposed to the radiation through 

 a fluorite window. At the end of half a second after 

 ignition the total quantity of heat radiated and recorded 

 by the bolometer amounted to 22 per cent, of the heat of 

 combustion of the gas. At this period the gas was still 

 radiating heat to a perceptible amount, its temperature 

 being then 1000° C. At the moment of maximum pressure 

 (1/20 second after ignition) 3 per cent, of the heat of 

 combustion had been radiated away. The radiation re- 

 corded by the external bolometer exceeds by about 50 per 

 cent, the difference between the heat absorptions by the 

 blackened and polished silver respectively. The estimate of 

 the latter difference is, however, subject to a good deal of 

 uncertainty on account of the large correction for heat k)st 

 to the backing to which the bolometer strip is fixed. More- 

 over, there are reasons for supposing that it does not 

 represent the whole of the radiated heat. 



Royal Microscppic*>l Society, Mav 2C. — ^^r. A. N. 

 Disney, vice-president, in the chair. — Dr. M. D. Ewreli : 

 Comparative micrometric measurements. — E. Heron-Allon 

 and A. Earland : The recent and fossil Foraminifera of 

 the shore sands of Selsey Bill, Sussex, part v., the Cre- 

 taceous Foraminifera. 



i>hvsical Society, Mav 27.— Prof. H. L. Callendar, 

 F.R.S.. president, in the chair.— Dr. W. H. Eccles : An 

 oscillation detector actuated solely by resistance-tempera- 

 ture variations. Experiments are offered as additional 

 support for the hypothesis of the mode of action of certain 

 types of electrical oscillation detectors. This hypothesis 

 suggests that in detectors constituted of a loose contact, the- 



