38 



NATURE 



[November 14, 1895 



The additions to the Zoblogical Society's Gardens during 

 the past week include a Western Slender-billed Cockatoo 

 {Lumetis pasinator) iiom Western Australia, presented by Mrs. 

 Halford Stephens ; a Crossed Snake {Psammophis crucifer), a 

 Hoary Snake (Coroneila cana), two Ring-hals Snakes (Sepedon 

 hitmachtes) from South Africa, presented by Mr. J. E. Matcham ; 

 a Common Wombat {Pkascolotuys wombat), a White-backed 

 Piping Crow ( Gymnorhin leuconota) from Australia, deposited ; 

 wo Pennant's Parrakeets {Platycercus pennanti) from Australia, 

 purchased ; a Rufous Rat Kangaroo {Hypsiprynintis rufescens), 

 a Red Kangaroo (Macropiis rtifus), born in the Gardens. 



, OUR ASTRONOMICAL COLUMN. 



The Temperature of the Sun.— Ebert's recent estimate 

 of the solar temperature (Nature, vol. Hi. p. 232), based upon 

 Langley's energy curves for heated solid bodies, is called in 

 question by Dr. Paschen {Astrophysical Journal, vol. ii. p. 202). 

 It appears that certain precautions have not been taken in 

 formulating the law derived from experimental data, and that 

 consequently the law does not hold even for the limits of tem- 

 perature between which direct observations can be made. The 

 chief defects of the former evaluations is that the prismatic 

 energy curves have not been transformed into those for the 

 normal spectrum ; and when this is taken into account, the sup- 

 position that the wave-length of maximum energy is inversely 

 proportional to the square root of the absolute temperature falls 

 to the ground. 



From a series of experiments made with the object of further- 

 ing theoretical investigations. Dr. Paschen considers it extremely 

 probable that " the wave-length of the maximum of energy in the 

 spectrum of an absolutely black body is inversely proportional to 

 the absolute temperature." Assuming provisionally as the 

 quantitative results of his observations, wave-length of max. 

 energy x absolute temp. = 2700, and adopting Langley's value 

 of o/i"5 (/u = 'ooi mm.) for the position of maximum energy in 

 the normal solar spectrum, Dr. Paschen finds the solar tempera- 

 ture to be 5400° on the absolute scale, or 5130° C. This means 

 that the sun gives an energy spectrum which is the same as that 

 of an absolutely black body at 5130° C. ; and this would be its 

 temperature if its light were entirely a consequence of its heated 

 condition, and if its surface possessed no selective reflection. 

 Attention is drawn to the fact that as our experimental methods 

 are improved, our estimates of the magnitude of the sun's tem- 

 perature are reduced. Dr. Paschen's value is more than a 

 thousand degrees lower than that of Messrs. Wilson and Gray. 



The Double Star 02"285. — Dr. See, to whom we are in- 

 debted for the revision of the orbits of so many double stars, has 

 lately given us another in the case of 02'285 {Ast. /our. No. 356). 

 We are almost tempted to ask whether any practical good results 

 from the premature attempt to determine an orbit where in- 

 sufficient observations ex-ist, or where the chance errors of 

 observations mask the apparent path of the star. Of course, 

 one very practical value such inquiries may have, especially in 

 the case of a close double star, is to point out the times when 

 observations are likely to prove possible and effective. But the 

 question arises, whether an elaborate interpolation formula or 

 real elliptic elements are dealt with. We are the more con- 

 cerned to put this question, because Dr. See himself points out 

 that Mr. Gore has, from practically the same observations, given 

 elements strikingly at variance with those to which he has been 

 conducted. The more conspicuous differences between the two 

 sets of elements are shown below. 



Gore(i845-i892). 866(1845-1895). 



Period ... 118 "57 years ... 76 '67 years 



Excentricity . . . 0*58 ,, ... 0-470 ,, 



Node ... 106^-58' ,, ... 62°-2 ,, 



Inclination ... 45*42 ,, ... 41*95 ,, 



The difficulty of deciding which of the two orbits is the more 

 probable representation of the motion is increased by the fact, 

 that the position angle computed from both is very similar. 

 Previous to 1865 and subsequent to 1887 (in the interval 1865- 

 87, the observations were very uncertain, owing to the close 

 approach of the components) the position angles computed from 

 the two orbits for the same date are rarely separated by a 

 -degree, while occasionally the observations differ from the 



NO. 1359, VOL. 53] 



computed place by as much as ten degrees. Dr. See gives an 

 ephemeris for the next five years, and if trustworthy observations 

 can be made of stars separated by about o"'3, additional light 

 will be thrown on the motion of this interesting pair. 



The Spectrum of a Aquil/e.— The fact that the lines in 

 the spectrum of a Aquilae are much broader than the correspond- 

 ing lines in the majority of stellar spectra, was first noticed by 

 Prof. Pickering, who suggested that this appearance might be 

 due to a very rapid rotation of the star. Photographs taken at 

 Kensington and Potsdam have also shown this haziness of the 

 lines. 



The spectrum of this star has formed the subject of a some- 

 what extended research by M. Deslandres at the Paris Observa- 

 tory, and h)y the use of a comparison spectrum enabling him to 

 determine the velocity in the line of sight, he has obtained results 

 of great interest {Comptes retidus, Nov. 4, p. 629). He finds 

 that very frequently there are fine double bright lines running 

 through the middle of the dark lines of hydrogen, and even some- 

 times through those of iron and calcium ; the brightness of the.se 

 lines varies with respect to the general intensity of the spectrum, 

 and M. Deslandres attributes them to the chromosphere of the 

 star. 



Measurements of the radial velocity are given for fifty-.six 

 dates, and they clearly indicate periodic but complex variations. 

 The maximum velocity of approach with respect to the sun was 

 38*4 km. per second on September 19, 1892, and of recession 

 1 1 "4 km. per .second on July 25, 1895. There appears to be a 

 great oscillation with a maximum velocity every forty-three days, 

 and superposed on this are one or more secondary oscillations, 

 one of which has probably a period of about five days. M. 

 Deslandres believes his results to indicate that Altair is at least 

 a spectroscopic triple star ; but he states that for a more complete 

 knowledge of the phenomena, better apparatus and a less variable 

 sky than that of Paris will be necessary. 



/3 Ursse Minoris also exhibits rapid fluctuations of velocity, 

 and M. Deslandres' results in connection with this star will form 

 the .subject of a future paper. 



Variability of Red Stars. — In the current number of 

 Knowledge, Dr. Brester gives a general account of his theory as 

 to the cause of variability in red stars (see Nature, vol. xxxix. 

 p. 492), and extends it a. step in order to account for the appear- 

 ance of bright lines. It is assumed that the Stars in question are 

 cooling bodies, and that the atmospheres are sufficiently cooled 

 down to permit the existence of chemical compounds. When 

 some of the vapours are cooled to the dew point, they will con- 

 dense in obscuring clouds, and produce a minimum without any 

 reduction of temperature. In addition to saturated vapours, if 

 we follow Dr. Brester, the atmospheres will also contain mole- 

 cules of dissociated matter, which will only combine after the 

 condensation of the saturated vapours has rendered the mixture 

 sufficiently concentrated. The combination of the dissociated 

 molecules produces heat enough to vapourise the clouds, and the 

 maximum is restored by the opening to view of the constantly 

 glowing interior. The presence of bright lines in the spectrum 

 of a variable star near maximum is ascribed to " luminescence " 

 produced by the chemical combination of the dissociated mole- 

 cules. Thus, the bright lines at the maximum, according to Dr. 

 Brester, are not the effect of heat, but rather of cooling. Dr. 

 Brester finds some justification for this supposed origin of bright 

 lines in the fact that carbon bisulphide gives a discontinuous 

 spectrum at no higher a temperature than 150°; but it must be 

 remembered that the bright lines in question are usually those of 

 hydrogen, and there is no experimental demonstration that these 

 lines can be produced except at a high temperature. To us 

 it seems easier to regard the bright ' lines of hydrogen as being 

 produced by true elevations of temperature about the time of 

 maximum, such as are explained by the meteoritic hypothesis. 



TYPHOID FEVER EPIDEMICS IN AMERICA. 

 T^HE factors which control the dissemination of disease are so 

 numerous, and in many cases so complicated, that it is 

 often only after long and patient searching that an epidemic is 

 successfully tracked to the original nidus from which it has 

 sprung. 



By the careful record of data of this description, compiled with 

 accuracy and care, we shall gradually become possessed of trust- 

 worthy material out of which an historical survey may be built 

 up, and the task of deciphering the course and conduct ;of 

 epidemic diseases materially lightened. 



