5oS 



NA TURE 



[February 24, 1910 



weight of the scattering material. (3) The most probable 

 angle of scattering increases rapidly with decreasing 

 velocity of the o-particles. — Dr. H. Geiger : The ionisation 

 produced by an a-particle. Part ii., Relation between 

 ionisation and absorption. Experiments are described 

 which were undertaken to measure the velocity of the 

 a-parlicles after passing through various sheets of mica of 

 known stopping power. A thin wire, which was made 

 hig-hly active by the deposit from radium emanation, served 

 as source of radiation. The a-particles emitted from it 

 passed through a narrow slit and produced a small line of 

 scintillations on a zinc sulphide screen. The deflection of 

 the line in the magnetic field amounted to i cm. and more, 

 and could be accurately measured by means of a travelling 

 microscope. The relative velocities found in this way when 

 different sheets of mica were interposed were up to 6 cms. 

 of the range in good agreement with those previously 

 obtained by Prof. Rutherford by a photographic method. 

 Great difficulties were experienced in observing the scintilla- 

 tions when the o-particles had to pass through a thickness 

 of mica nearly equivalent to the range. It could, however, 

 be shown that the velocity decreased rapidly towards the 

 end of the range. The lowest velocity which was measured 

 corresponded to o'27 of the initial velocity. The a-particlos 

 had in this case to pass through a thickness of mica 

 equivalent to 6-8 cm. of air. The experimental results 

 could be represented with good approximation by the equa- 

 tion 7)' = a (R — x), where a and R are constants, R denoting 

 the maximum range of the a-particles. The curve indicates 

 that the velocity becomes zero at the end of the range. In 

 the course of the experiments an investigation was carried 

 out to see whether all the o-particles from radium C arf 

 emitted with identical velocities. The experiment showed 

 that the variation in the initial speed, if any, was certainly 

 less than o"5 per cent., but that the a-particles acquired a 

 slight difference in velocity in passing through air. Assum- 

 ing that the ionisation produced by an a-particle is propor- 

 tional to the expenditure of energy, the equation repre- 

 .senting the ionisation at any point of the path can he 

 deduced from the above equation for the velocity. Taking 

 into account the slight variation of velocity in a pencil of 

 a-particles at the end of the path, the theoretical ionisation 

 curve agrees fairly well with the experimental. — H. C. 

 Greenwood : The influence of pressure on the boiljng 

 points of metals. The present research is a continuation of 

 a previous paper dealing with the boiling points of metals 

 under atmospheric pressure. Previous work at reduced 

 pressures has been strictly limited by the lack of any 

 material capable of maintaining a vacuum at high tempera- 

 ture, being, in fact, confined, except for a few metals of 

 relatively low boiling point like zinc, to some observations 

 in a very high vacuum. For similar reasons nothing has 

 been done on the effect of high positive pressures. The 

 difficulties here indicated were avoided by arranging the 

 whole furnace inside an enclosure in which the desired 

 changes of pressure could be produced. Heating was 

 effected electrically, and the temperatures were measured 

 optically, while the actual boiling point determinations were 

 made by a method of visual observation similar to that 

 before used. Observations were taken at pressures ranging 

 from 100 mm. of mercury to 50 atmospheres. The order of 

 magnitude of the effects produced is shown by the following 

 example : — The boiling point of bismuth under 102 mm. of 

 mercury is 1200° C, and under t6'5 atmospheres 2060° C, 

 a variation of 860° being thus produced. The boiling points 

 of all the metals studied (bismuth, copper, lead, silver, tin, 

 zinc) were found to show a closely similar dependence (in 

 the pressure. — S.. O. Rankine : The viscosities of the gases 

 of the argon group. The viscosities of the five gases — 

 helium, neon, argon, krypton, and xenon — have been com- 

 pared with that of air. The method used was that de- 

 scribed in a paper recently communicated to the society. 

 The principal advantage of this method is that it enables 

 the viscosity of quite a small quantity of gas to be deter- 

 mined with considerable accuracy. The total volume of 

 the apparatus used in this case was rather less than 6 c.c. 

 The values found for the viscosities of helium and argon 

 are in close agreement with those obtained by previous 

 observers. The results for the remaining three gases admit 

 of no comparisons, these being the first determinations. 

 NO. 2104, VOL. 82] 



.Ml five gases are more viscous than air, the ratios ij/i; air 

 being as follows : — 



I 0S6 



1721 



1-361 



I '234 



The viscosity of noon at ordinary temperature is far higher 

 than that of any other gas hitherto experimented upon, and 

 krypton is next in order of magnitude. As the atomic 

 weight increases the viscosity alternately rises and falls. 

 If, however, the mean free paths are calculated by using 

 Maxwell's equation, they are found to decrease regularly 

 with increase in atomic weight. The paper also contains 

 estimates of the relative sizes of the atoms and their 

 densities, the calculations being based upon the kinetic 

 theory of gases. The conclusions arrived at are that the 

 densities of the atoms of neon, krypton, and xenon are the 

 same, and three times as great as that of helium. The 

 argon atom is nearly twice as dense as the helium atom. 



Physical Society, February 11.— Dr. C. Chree, F.R.S., 

 president, in the chair. — Prof. H. L. Callendar : Presiden- 

 tial address. The application of resistance thermometers 

 to the recording of clinical temperatures. The objections 

 to thermocouples are twofold. The E.M.F.'s developed are 

 so small that the recording instruments must be very sensi- 

 tive and therefore unsuitable for ordinary use. Serious 

 difficulties arise with regard to the thermostat necessary to 

 maintain one of the junctions of the thermocouple at a 

 constant temperature. The chief difficulty in connection 

 with the use of resistance thermometers lies in the heating 

 effect of the current. It was pointed out that in platinum 

 thermometry, to obtain accurate compensation for the re- 

 sistance of the leads, it is necessary that the ratio arms 

 of the Wheatstone bridge should be equal, and it was 

 shown that this condition reduced the sensitiveness to be 

 obtained by suitably varying the resistances by about 30 

 per cent. In joining up a bridge in work with resistance 

 thermometers. Maxwell's rule for the positions of the battery 

 and galvanometer which give maximum sensitiveness is 

 seldom applicable. While Maxwell's arrangement actually 

 gives the greatest sensitiveness, the heating effect of the 

 current is so much greater that this more than counter- 

 balances the increased sensitiveness. The problem to be 

 solved in designing a suitable thermometer for clinical work 

 is, with a given galvanometer and resistance-box, to find 

 the resistance of the thermometer which will give the most 

 accurate results for a given heating effect of the current. 

 This is given by the equation R = 2G-|-S, where G is the 

 resistance of the galvanometer and S that of one of the 

 ratio arms. It is important in the construction of a ther- 

 mometer for clinical work to secure quickness of action 

 and to reduce the heating effect of the current. An ordinary 

 tube-form of thermometer is good for laboratory work with 

 sensitive galvanometers, but it is unsuitable for use with 

 recorders. The pattern of the thermometer must be suited 

 to the purpose for which it is intended. Three types were 

 shown, designed for mouth, rectal, and surface work. Con- 

 tinuous records obtained from a patient with a normal tem- 

 perature were shown. The temperature is generally very 

 steady if the thermometer does not shift or the patient get 

 wholly or partly out of bed. The effects of external changes 

 of temperature were also shown, and simultaneous records 

 taken on different parts of the body illustrated the fact that 

 the temperature does not vary in the same way at all places. 



Royal Meteorological Society, February 16. — Mr. H. 

 Mellish, president, in the chair. — E. Mawley : Report on 

 the phenological observations for 1909. During the whole 

 year wild plants came into blossom behind their usual 

 time, the departures from the average being greatest in 

 March and April. Such early spring immigrants as the 

 swallow, cuckoo, and nightingale made their appearance 

 rather earlier than usual. The only deficient farm crops 

 were beans, peas, and hay. On the other hand, the yield 

 of wheat, barley, oats, turnips, mangolds, and potatoes 

 was well above the average, and more particularly barley 

 and turnips. The crop of apples, pears, and plums was 

 under average, whereas that of raspberries, gooseberries, 

 currants, and strawberries, taken together, was fairly 

 good. As regards the farm crops, this was the fourth 

 vear in succession in which the vield has been above 



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