382 



NATURE 



[February 20, 1902 



are to survive. There will usually be in this second case, not 

 a single system, hut an indefinite number of systems which 

 would equally well fit individuals to survive ; in the first case, 

 on the other hand, there are an indefinite number of systems 

 which equally unfit their owners for surviving. This distinction 

 seems of considerable interest. 



For example, to select from the French race a race in femur 

 and humerus like the Aino, we should have to proceed by a 

 positive selection ; but to select from the Aino a race like the 

 French, we should have to proceed by a negative selection. To 

 get 1000 Aino we should have to select for these two organs 

 alone out of some 6,000,000 Frenchmen, but to get 1000 French- 

 men from the Aino we must select from about a billion of the 

 latter. Thus we are to some extent able to appreciate the 

 stringency of the selection, which even lasting through long ages, 

 and introducing continuous reproduction, would be needful to 

 enable us to pass in the case of only two organs from one race 

 to the other. Another point brought out by the surface of 

 survival-rates is the fact that the fittest to survive are usually 

 not the most frequent survivors. 



It will be seen that the memoir opens up a novel field of 

 in\-estigation, but one so wide that the theory of it must be 

 limited by close contact with what is needful for the purposes of 

 evolution. We want measurements on the local races of 

 animals to guide us ; at present we know scarcely in any one 

 case whether differentiation has taken place by direct selection 

 of few or of many organs. When once such measurements 

 are forthcoming we shall have firmer ground to go upon, and 

 the processes of the present memoir seem to suggest how in the 

 future we shall be able to link together quantitatively local 

 races, and possibly at a more remote date obtain quantitative 

 conceptions of the stages of evolutionary descent itself. 



January 30. — " The Specific Volumes of Oxygen and Nitrogen 

 Vapour at the Boiling-point of Oxvgen." By James Dewar, 

 M.A.,D.Sc., LL.D., F.R.S. 



In a paper on " The Boiling-point of Liquid Hydrogen deter- 

 mined by Hydrogen and Helium Gas Thermometers " the author 

 pointed out that a constant-volume gas-thermometer filled with 

 oxygen gas, having a pressure at 0° C. of about Soo mm., gave a 

 very accurate value of the boiling-point of liquid oxygen. As it 

 seemed advisable to confirm this result indirectly, an attempt 

 was made to determine the vapour density of oxygen at its 

 boiling-point by direct weighing, the intention being, if the 

 experimental results proved at all encouraging, to repeat the 

 work on a larger scale and with greater precautions. As at 

 present there is no likelihood of the more accurate determina- 

 tions being made, the results of the preliminary inquiry are 

 presented to the .Society. They give in any case, with con- 

 siderable accuracy, the specific volumes which have never been 

 directly determined. 



In order to obviate any question of the buoyancy of 

 the air, two flasks A and B of as nearly as possible the 

 same air displacement were counterpoised -on an OErtling 

 balance. The B flask remained permanently on one scale of 

 the balance during all the weighings, while the A flask was 

 weighed, either exhausted or filled with oxygen (or nitrogen), in 

 various circumstances according as the experiments required. 



As the intention was not only to ascertain the density of 

 oxygen and nitrogen at their respective boiling-points under 

 atmospheric pressure, but also under diminished pressure, ex- 

 periments were made with nitrogen at ordinary tem- 

 peratures and at pressures varying from about one-sixth of an 

 atmosphere to ordinary pressures, in order to find the range of 

 variation in the results with the 316 c.c. flask to be used in the 

 subsequent low-temperature experiments. 



Experiments with nitrogen give a mean value of I '260 

 grammes, at standard temperature and pressure, as the 

 weight of a litre of the gas. This is about a quarter 

 per cent, higher than the accepted value of I "257. The 

 extreme variation in the individual experiments is about 

 half a per cent. The average value of the results under 

 about one-third of an atmosphere is I '266 grammes, the ten- 

 dency under the low pressures being to make the density half a 

 per cent, higher. Considering that in the actual low-tempera- 

 ture experiments the mass ol gas to be weighed would be at 

 least three limes greater, it was inferred that in spite of difii- 

 <:ullies of manipulation and corrections, the results might be 

 anti_ci])ated to lie within a half per cent, of the true value. 



The mean weight, given by six experiments, of one litre of 

 oxygen vapour at 7C0 mm. and 90°-5 absolute was found to be 



NO. 1686, VOL. 65] 



4'420 grammes, and the specific volume 22625 c.c. If the 

 first two experiments are eliminated on the assumption that the 

 proper equilibrium of temperature had not been attained, the 

 average weight per litre would become 4*428 grammes, and the 

 specific volume 225 '82. 



Taking Regnault's density of oxygen at 0° and 760 mm., 

 the density at 90°'5 in the ordinary way would be 0"0O43i37, 

 and the specific volume 231 '82 c.c. Thus the volume given by 

 the ordinary gaseous laws is f0246 times the average observed 

 volume ; or we may put it that pi> is diminished at the boiling- 

 point of oxygen by 2*46 per cent. Again, while the ratio of 

 the absolute temperatures is 3'oi7, the ratio of the densities is 

 3 09I- 



Further experiments were made on oxygen vapour at 90°*5 

 and under reduced pressures. If the first three experiments 

 are averaged (the pressures being close together), the weight 

 of a litre of oxygen at 90°'5 absolute under a pressure 

 of 282'5 mm. would be I 5982 grammes. The ratio of 

 this density to the value previously found for one atmo- 

 sphere pressure, viz. 4*42 grammes, is 2765, and the ratio of 

 the pressures is 2 '690. It appears that the ratio of the change 

 of density of the vapour of oxygen at 90' '5 absolute, under 

 variable pressure, is greater than the ratio of the change of 

 pressure. It is clear, however, that it would be necessary to 

 work upon a larger scale in order to get satisfactory vapour 

 densities at low temperatures under pressures below that of the 

 atmosphere. 



Observations were made on the density of nitrogen vapour at 

 the boiling-points of liquid oxygen and liquid air respectively. 



Two experiments were made with liquid oxygen taken to 

 be at temperature 90°"5 absolute. Four experiments were 

 made in one and the same sample of liquid air, with rising 

 temperature. The first two experiments made with liquid 

 oxygen give a ratio of the nitrogen densities from the author's 

 own values of 3'o8S, the absolute temperature ratio being 3'0I7, 

 his values for the ratio of the oxygen densities for the same 

 range of temperature being 3'09i as previously deduced. It 

 may be safely assumed that if the density of nitrogen were 

 observed at its boiling-point it would deviate as much from the 

 ordinary gaseous laws as oxygen. Further, the specific volume 

 of nitrogen at its boiling-point of 7S' absolute would from the 

 above formula be 221 '3 as compared with 226"2, the similar 

 value found for oxygen. 



The general inference to be drawn from these preliminary 

 experiments is that trustworthy vapour densities may be 

 determined at very low temperatures. There seems to be 

 no reason why the vapour density of hydrogen at its boiling- 

 point should not be accurately ascertained ; only, as in 

 this case the internal pressure in the weighing fiask would 

 amount to nearly fifteen atmospheres, it would be advisable to 

 construct the flask of some metal or alloy. A fl.ask of the size 

 used in the oxygen experiments filled with the vapour of 

 hydrogen at its boiling-point would be equivalent in weight to 

 between four and five litres of hydrogen at the ordinary tem- 

 perature and pressure, and such an amount of material ought to 

 give density results at the boiling-point of hydrogen of con- 

 siderable exactness, notwithstanding the great manipulative 

 diflkultics that would neces.sarily be involved in the execution 

 of such a determination at 21° absolute. 



Physical Society, February 14. — Annual General Meeting. 

 — Mr. T. H. BUikesley, vice-president, in the chair. — Prof. 

 S. P. Thompson, F. U.S., was re-elected president. Prof. S. P. 

 Langley and Prof H. A. Lorentz were elected honorary 

 fellows to fill the vacancies caused by the deaths of Prof. 

 Rowland and Ur. Koenig. The president of the German 

 Physical Society was elected an exofficio fellow of the Society. 

 — The secretary then read the president's address. It com- 

 menced by giving some particulars of the life and work of 

 Rowland, Koenig, Langley and Lorentz. On January 1 1 a 

 telegram was sent, in the name of the Society, to I'rof. Ilittorf 

 congratulating him upon the jubilee of the professoriate. The 

 work of translation, revision and production of an English 

 version of Gilbert's " De Magnete " has been completed, and 

 a copy of the book presented to the Society by the president. 

 The remainder of the address dealt with the refusal of the law 

 of this country to recognise as valid matter for the granting of 

 letters patent anything which may have been brought before 

 any of the learned or .scientific societies. In the United States 

 a man may appeal to the fact of his having read such a paper in 

 proof of his subsequent claim to receive a valid patent for his 



