October i8, 1906J 



NA TURE 



619 



<ier Erde." The second volume, dealing with salt in Asia, 

 Africa, America, and Oceania, appeared recently, and the 

 first volume-, which will be concerned with Europe, is in 

 the press. 



The prominence now given to geometrical and machine 

 drawing in the curricula of schools and colleges has led 

 to an increased demand for trustworthy mathematical 

 drawing instruments. The recent catalogue, with its 

 numerous illustrations, published by Mr. \V. H. Harling, 

 of Finsbury Pavement, London, showing the instruments 

 he is prepared to supply, may be commended to the atten- 

 tion of teachers and students. In it they will find par- 

 ticulars concerning a great variety of instruments designed 

 to meet every want. 



OVR ASTRONOMICAL COLUMN. 

 Co.MET i<)o6e (Kopff). — In addition to those publi.shed 

 by Herr M. Ebell, elliptic elements have been calculated 

 for the orbit of Kopff 's comet by Messrs. Crawford and 

 Champreu.x, and are published in No. lOO of the Lick 

 Observatory Bulletins. They are as follows : — 



Elements. 

 T=iqo6 May 2-0877 G.M.T. 



Epocli = 1906 Sei.t. 567091 ., log </ = 0-2301 14 



. . „ log <- = 97i6356 



M= 1841 546 log (7 = 0-549258 

 u= 19 2S 44 91 ,"=';32''255 



a =263 45 23 6 [-1906 o Period = 6 66633 years 

 /= 8 ^4 098 j 



The first decimal place of the period is determinate, and 

 as this agrees with Herr Ebell 's, who gave 6-()i7 years, it 

 may be taken as fairly established. An ephemeris which 

 accompanies. the elements gives the following positions for 

 the remainder of this month : — 



Ephemeris (12/1. G.M.T.). 



a (rue) S(true) .006 a (true) 



i (true 



Oct. 17-5 . 22 28 .5 3 Oct. 25 5 .. 22 30 ... 4 30 

 21-5 ... 22 29 ... 4 45 295 .. 22 32 ... 4 t7 



Ji'piter's Seventh S.^tellite. — From a telegram from 

 Prof. Pickering to the Kiel Centralstelle, published in No. 

 4123 of the Astroiiomisehe Xachrichtcii, we learn that 

 Jupiter's seventh satellite was re-observed by Prof. Perrine 

 at the Lick Observatory on September 25. The position- 

 angle and distance at 190b September 25-9962 were iig"-! 

 and 2578" respectively. 



OBSERV.4TIONS OF V.4RI.ABLE St.^rs. — Bulletin No. 8 of 

 the Laws Observatory, University of .Missouri, contains 

 the results of some variable-star observations made at the 

 observatory during iqo5-6. A grant of five hundred dollars 

 from the Gould fund of the National .Academy of Sciences 

 has enabled the director. Prof. F. H. Seares, to engage an 

 assistant observer, Mr. E. S. Haynes, for this work with 

 gratifying results. 



The star B.D. -I- 55°.28i7 has been shown to be a variable 

 of the continuous variation type, with a range of 0-4 magni- 

 tude and a period of 54 days. Observations of 

 V Lacertse, V Vulpeculse, and 108.1905 Capricorni are also 

 recorded. In the case of the last-named, the rise to 

 maximum is very rapid, an increase of 1-5 magnitudes 

 taking place in ij hours, and the observations show that 

 this star is probably not of the .Mgol type. 



Sun-spot Spectra Observatio.ns. — In No. 2, vol. xxiv.. 

 of the Astrophysical Journal, Mr. W. M. Mitchell, of 

 Princeton Observatory, records the results of his sun-spot 

 spectra observations made during the period October, 1005, 

 to May, 1006. Mr. Mitchell found that during th" more 

 recent observations the number of " weakened " lines in 

 the spot spectra has increased considerably ; many lines 

 previously recorded as " reversed '' are now " weakened," 

 and new lines of the latter type are recorded. .\ sugges- 

 tion that this change may be a result of the pasi^ing of 



the sun-spot maximum awaits the confirmation of further 

 observations. Numerous cases of abnormal " reversals " 

 are referred to in the paper. From the observations of 

 reversed lines .\Ir. .Mitchell deduces a temperature for the 

 gases producing these lines of 4700°, and a further deduc- 

 tion gives 0-38 as the ratio of the sun-spot radiation to the 

 radiation from the unaffected photosphere. The spectrum 

 and construction of the chromosphere are also discussed 

 at some length. 



NO. 1929, VOL. 74] 



CONDENS.ATION NUCLEL' 

 pROF. Barus has written more upon the subject of 

 condensation nuclei than any other physicist. In the 

 present memoir, as in those which have preceded it, he 

 arrives at conclusions which are not in agreement with 

 the work of others who have investigated the properties 

 of ions and nuclei. If his investigations are to be trusted, 

 the determinations which have hitherto been made of the 

 charge carried by the ions by means of the condensation 

 method must be regarded as quite untrustw-orthy. The 

 matter is of sufficient importance, therefore, to justify an 

 examination of Prof. Barus's methods. 



The first three chapters, and the greater part of the 

 sixth and concluding chapter, are concerned with e.xperi- 

 ments upon the production of clouds by the sudden ex- 

 pansion of dust-free air initially saturated with water 

 vapour, the air in most cases being exposed to the action 

 of X-rays or radium. As described by Prof. Barus, the 

 phenomena are exceedingly complicated and irregular. 

 This is not surprising, however, being largely a result of 

 complication in the experimental conditions. 



The expansion was brought about by suddenly opening 

 communication between the " fog chamber " and another 

 much larger, partially exhausted vessel, a measured fall of 

 pressure being thus produced. By means of the coronas 

 formed, an estimate was obtained of the size, and hence 

 indirectiv of the number of the drops ; filtered air was then 

 re-admitted to bring the pressure back to that of the 

 atmosphere. This method of effecting the expansion is not 

 a suitable one for investigations of the kind attempted. 

 For the rate of fall of pressure must diminish as the ex- 

 pansion approaches completion ; it is probable that with 

 a suitable width of connecting tube no great error will be 

 introduced into the measurement of the least expansion 

 required to produce a cloud [i.e. that the expansion may be 

 made practically adiabatic), but it is unlikely that the 

 maximum degree of supersaturation resulting from ex- 

 pansions greater than this approaches at all closely to that 

 calculated from the pressure fall. For the condensation on 

 the nuclei which first come into action will, by reducing 

 the amount of vapour remaining uncondensed and by the 

 heat set free, prevent the full supersaturation corresponding 

 to the pressure fall from being attained. The larger the 

 number of easily caught nuclei, the more will the maxi- 

 mum supersaturation attained fall short of the theoretical. 

 The method is thus not a suitable one for obtaining in- 

 formation about the number of nuclei corresponding to 

 various degrees of efficiency. 



If we produce a cloud in dust-free air upon nuclei which 

 require a high degree of supersaturation to make water 

 condense upon them, the drops which are formed, if caused 

 to evaporate bv compression of the air, appear to leave 

 behind nuclei requiring only a slight supersaturation to 

 make water condense upon them. Unless these are re- 

 moved before expansions large enough to catch the original 

 nuclei are again attempted confusion is sure to follow. 

 The result of" neglecting this precaution is not merely that 

 these residual nuclei give rise to drops as well as those 

 under investigation, but unless the apparatus is such as 

 gives exceedinglv efficient expansion the supersaturation 

 necessarv for the capture of the nuclei under investigation 

 mav not he attained, the number of drops produced being 

 thus too small in contrast to what might at first sight be 

 expected. The experiments of Prof. Barus's investigation 

 were performed under conditions which made this effect 



1 " Tlie Nudeation of the Uncontaminated AtmosDhere." Pv Prnf. Carl 

 Rarus. Pp. 152. (Published by ihe Cirnegie Institution of Washington 

 January. 1906.) 



