NA TURE 



[July i, 1909 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous communications.] 



Diurnal Variation of Temperature in the Free 

 Atmosphere. 



The following results, which I have recently obtained 

 by a discussion of temperatures obtained in kite and 

 captive balloon ascents, may be of interest in connection 

 with Prof. Clayton's letter (Nature, February 4) and Mr. 

 Dines's remark that at a height of 1 km. the daily tempera- 

 ture variation becomes insignificant (Nature, June 17). 

 The daily variation of temperature at a height of i km. 

 over Berlin, deduced from 2232 observations made during 

 the five years 1903-7, is given in degrees C. by 



T = Tj- (4-40 + ooS) + (o'87 + o-i3) i-in (;;/ + e,)-l-(o-!4 + o-io) 



sin(2H/ + e.,\ 

 where T, is the mean surface temperature, and the prob- 

 able errors are deduced by the method of least squares. 

 The most probable values for 9,, f),, are 197° and 123" 

 respectively, the time being measured from midnight. 



The variation deduced from 962 observations, made 

 during the four years 1903-6, in which the wind at a 

 height of I km. was 8 metres per sec. and upwards, is 

 given by 



T = T,-(3-97±o-i5)-Ko-S4 + o-23)sin(H/ + 9,') + (o-35 + o'i5) 



sin [zirf + g./). 



The most probable values of fl,, 0,, are 173° and 102° 

 respectively. 



The close agreement in the values for the amplitude of 

 the whole day wave for the two cases proves that there 

 is no large error due to the influence of solar radiation 

 on the instruments, and that the variation is a real varia- 

 tion of the temperature of the atmosphere. 



The mean daily range is, then, 1-7° C. (or 3-1° F.), com- 

 p.-ired with a mean daily range of about 5° C. at Kew, 

 where the temperature variation is given by 



T = T, -^ 2 -56 sin (it/ + 226°; -1- 0*42 sin (2;// 4- 45°). 



The maximum temperature at a height of i km. appears 

 to occur from two to three hours later than at the surface 

 in the whole day wave, and two to three hours earlier 

 in the semi-diurnal wave. 



The variation at a height of 2 km., deduced from all 

 (1132) observations, is given by 

 T = T,- (98410-23) 



+ (o-64 + o-3i) sin (H;'4-e]) + (o-25 + o-23) sin {2it/ + g.-,), 



the most probable values for »,, »,, being 270° and 72° 

 respectively. 



The magnitude of the probable errors precludes the 

 results from being regarded as final. More observations 

 are needed. But it appears certain that we do not get, on 

 this side of the Atlantic, the remarkable diminution in 

 amplitude and change of phase in the diurnal component 

 which Prof. Clayton found In the first 1000 m. at Blue 

 Hill. The amplitude of the semi-diurnal component does 

 show an increase at 2 km. over its value at i km., but, 

 having regard to the relatively large probable errors, one 

 cannot attach any real significance" to the result. At the 

 same time, it is of Interest to find that at i km. and 

 2 krn. altitude In these latitudes the temperature varia- 

 tion is as great as It is over the ocean near the equator, 

 where the value of the daily range is about 1-5° C. 



Cambridge, June 20. E. Gold. 



Temperature of the Upper Atmosphere. 



An explanation of the existence of an isothermal layer 

 may possibly be found in the fact that carbon dioxide 

 condenses and freezes at low temperatures even when the 

 pressure Is low. The strata in which CO, circulates, fall- 

 ing as small drops and then evaporating", must be com- 

 parable in the irregularity of their temperature gradients 

 with the strata near the earth in which water circulates. 

 The temperature of the bottom of the mist of CO., must 



NO. 2070, VOL. Si] 



be approximalely a function of the pressure, so it is to 

 be expected that the height of the mist will vary from 

 day to day and from place to place. In particular, it 

 appears that the change of temperature gradient should 

 occur in the tropics at a greater altitude and lower tempera- 

 ture than elsewhere. The observations to which Mr. Cave 

 refers (Nature, June 17) confirm this part of the theory. 



F. J. W. WinpPLE. 

 Merchant Taylors' School, E.C., June 28. 



The Aeronautical Society. 



In reference to Prof. Bryan's remarks on the aims and 

 objects of the Aeronautical Society of Great Britain in 

 Nature of May 27, I would point out that the general 

 scientific character of the proceedings vf a society is not 

 annulled because one or more writers have fallen into 

 error, any more than it would be reasonable to say that 

 Prof. Bryan is not a profound mathematician because, in 

 a Friday evening discourse at the Royal Institution, he 

 fell into inaccuracy In scientific history, and said that 

 the Aeronautical .Society of Great Britain was at one 

 time called the Balloon Society, and changed its name 

 to its present title, the fact being that the Balloon Society 

 was quite a separate affair, which had its meetings at 

 the Westminster Aquarium and discussed every subject 

 under the sun. In that remark Prof. Bryan showed he 

 had not closely followed the work and career of the 

 Aeronautical Society of Great Britain. 



During my eight years of honorary secretaryship of 

 the society, amongst the readers of papers and those who 

 made communications will be found Dr. W. N. Shaw, 

 F.R.S., Mr. W. H. Dines, F.R.S., Prof. C. V. Boys, 

 F.R.S., the late Prof. G. F. Fitzgerald, F.R.S., Prof. 

 Bryan himself. Sir Hiram Maxim, Mr. Lawrence Rotch. 

 Dr. Hergesell, Mr. F. H. Wenham, Captain R. F. Scott, 

 Lieut. E. H. Shacklcton, Mr. Orville \^'rlght, Mr. Charles 

 Harding, Mr. W. F. Reid, &-c. These names vouch for 

 the general high standard of the proceedings of the society 

 in recent years. 



While making these criticisms on Prof. Bryan's re- 

 marks, I sincerely hope he will continue his own epoch- 

 making aeronautical researches, for the sake of aero- 

 nautical science and for the honour of the Aeronautical 

 Society, of which he Is a member. 



Airth, Sunningdale, June 14. Eric Stuart Bruce. 



I HAVE no desire to do injustice to the .Aeronautical 

 Society, neither do I expect its proceedings to be free 

 from all errors. But in view of the fact that mathe- 

 matical fornuiL-e and physical considerations now fre- 

 quently enter into papers bearing on aeronautics, I con- 

 sider that the time has come when the society should 

 realise the importance of dealing more efficiently with 

 papers of a theoretical character than was necessary 

 formerly. As I have communicated my views on this 

 point to the society through Mr. Bruce, a detailed reply 

 may be unnecessary. 



I do not wish all aeronauts to be profound mathe- 

 maticians. I consider that papers dealing with practical 

 aeronautics have been the most valuable feature of the 

 society's work. Many of the eminent writers to whom 

 Mr. Bruce refers have dealt with the practical and ex- 

 perimental rather than the theoretical side of the subject. 

 Further, a distinction must be drawn between Inaccuracies 

 made in discourses or discussions at meetings and those 

 which are allowed to find their way uncorrected into print. 

 But when papers are published in a scientific society's 

 journal which deal with questions of a theoretical character 

 or contain formulae, it is not unreasonable to expect that 

 the authors shall correctly state and properly apply such 

 principles of mathematics, physics, and mechanics as are 

 found in ordinary text-books, and I trust that, as the 

 result of this correspondence, the exceptions will be less 

 frequent in the future than they have been in the past. 



May "T, in answer to very numerous inquiries, state 

 with regret that it has been impossible, as yet, to publish 

 a detailed account of my Royal Institution lectures, and 

 some time will elapse before the work in which I am 

 interested Is in a suitable form for publication? 



G. H. Bryan. 



