December 2, 1897] 



jVA TURE 



lOl 



Critical Temperature of Water. 



In answer to Mr. Martin's letter in your last issue (p. 80), 

 Cailletet and Colardeau found the critical temperature of water 

 to be 365" C, the corresponding pressure being 200*5 atmos. 

 An account of their experiments is given in Preston's " Theory 

 of Heat," p. 384. S. Geo<;hegan. 



Dublin. November 29. 



SPECTRUM OF A METEOR} 



THE photographs of the spectra of the stars taken at 

 the Harvard College Observatory as part of the 

 Henry Draper Memorial differ in two respects from 

 those ordinarily taken elsewhere. Instead of using a 

 spectroscope with a slit, in which but one star is photo- 

 graphed at a time, a large prism is placed over the 

 object-glass of the telescope, and thus spectra of all the 

 bright stars in the field of view are obtained. The 

 number of stars photographed simultaneously is still 

 further increased by substituting for the object-glass a 

 portrait lens like that used by photographers, only 

 larger. The field of view is in this way increased from 

 two degrees square to ten degrees square, and a photo- 

 graph IS obtained of the spectra of all the brighter stars 

 in this large region. Many thousand plates, covering 

 the entire sky, have been taken in this way at the 

 Cambridge and Arequipa Stations of this Observatory. 

 All have been examined by Mrs. Fleming, and, as a 

 result, numerous remarkable objects have been dis- 

 covered. One of the latest is the spectrum of a meteor 

 which has thus been photographed for the first time. 

 Since it is impossible to foresee when the bright meteors 

 will appear, or what path they will follow, a photograph will 

 be obtained only when one happens to cross the field 

 of the telescope. A number of trails of meteors have 

 been obtained, both here and elsewhere, when charts of the 

 stars were photographed, no prism being used. When 

 the prism was in place no meteor bright enough to leave 

 a noticeable trail has heretofore been photographed on 

 the many thousand plates examined. At about 1 1 p.m. 

 on June 18, 1897, however, when the 8-inch Bache 

 telescope at Arequipa was directed towards the con- 

 stellation Telescopium, a bright meteor appeared in 

 right ascension i8h. 19m., declination -47° 10', and 

 passed out of the field at right ascension i8h. 29m., 

 declination - 50^ 30'. The spectrum consists of six 

 bright lines whose intensity varies in different portions 

 of the photograph, thereby showing that the light of the 

 meteor changed as its image passed across the plate. 

 The approximate wave-lengths of these lines are 3954, 

 4121, 4195, 4344, 4636, and 4857, and their intensities 

 are estimated as 40,100, 2, 13, 10, and 10, respectively. ! 

 The first, second, fourth, and sixth of these lines are 

 probably identical with the hydrogen lines Hf, HS, Hy, 

 and H/3, whose wave-lengths are 3970, 4101, 4341, and 

 4862. The fifth line is probably identical with the band 

 at wave-length 4633, present in spectra of stars of the ! 

 fifth type and forming the distinctive feature of the third ; 

 class of these stars. The third line, which is barely ' 

 visible, is perhaps identical with the band at wave-length 

 4200, contained in these stars {Astron. Nach. 127, p. i). 



It will be noticed that of the four hydrogen lines in 

 the spectrum of the meteor, H6 is the most intense. 

 This is also the case in the spectrum of o Ceti and of 

 many other variable stars of long period. In some 

 variables of long period HS and Hy are equally intense, 

 while in others Hy is the more intense. In some stars of 

 the first type in which the hydrogen lines are bright, | 

 like y Cassiopeiae, the line H/3 is much more intense in 

 the photographic spectrum than any of the other lines, ' 

 while in the spectra of stars like P Cygni and ij Carinas, I 

 H8, Hy, and H^ are nearly equally bright. These I 



1 Harvard College Observatory. Circular No. 20. 



NO. 1466, VOL. 57] 



results show an important resemblance between meteors 

 and stars having bright lines in their spectra, and may 

 aid in determining the conditions of temperature and 

 pressure in these bodies. Since bright meteors some- 

 times appear during the November meteoric shower, a 

 special effort will be made to obtain photographs of 

 them, both trails and spectra, on November 1 3. 

 November 8. Edward C. Pickering. 



GEOLOGY AND SANITARY SCIENCE. 



"T^HE address recently delivered by Mr. W. Whitaker^ 

 -*■ F.R.S., before Section iii. of the Congress of the 

 Sanitary Institute {Journal of fhe Sani/ary Ins/t/uie,\o\: 

 xviii., 1897, pp. 304-316), touches upon several matters 

 of special interest at the present time. Section iii. 

 deals with chemistry, meteorology, and geology, and 

 Mr. Whitaker chose for his subject "Water," as being 

 appropriate for such a triple alliance. Most important 

 is his suggestion " that round each work for the public 

 supply of water a certain tract of the water-bearing bed 

 should be saved from the assaults of surface-contamina- 

 tion." The address was delivered before the Maidstone 

 epidemic had occurred, but reference is made to it in a 

 postcript, and no stronger support for Mr. Whitaker's 

 proposal could have been given. He rightly observes 

 that '* we are yet without much information as to how- 

 far pollution may be able to reach along an underground 

 course," but " it is here that geology comes in, for the 

 nature of the surroundings of waterworks must be takerJ 

 into account, often for some distance and to some depth." 

 From a sanitary point of view the mapping of all the 

 surface deposits on the six-inch scale by the Geological 

 Survey is referred to as most necessary. A great deal 

 has been done, but very much more remains to be done ; 

 and, as Mr. Whitaker observes, "a survey of the drifts in 

 the London area on the six-inch scale is greatly needed." 

 It is a serious matter when sewage-farms and ceme- 

 teries are placed on porous strata, which are perhaps in 

 adjacent tracts utilised for their supply of water ; and yet^ 

 as Mr. Whitaker remarks, " sewage-farms and cemeteries 

 must exist, until some other methods of disposing of 

 waste material are not only found out, but are generally 

 adopted." 



Clearly there is need for greater control over the sites 

 chosen for any of the purposes mentioned, and public 

 sources of water-supply must be carefully safeguarded. 

 The question of federation in the matter of water-supply 

 in many localities is one to which attention is drawn, and 

 this also is becoming urgent. 



NOTES. 

 The French Government, through its Embassy in London^ 

 has presented to Sir Archibald Geikie a handsome vase of 

 Sevres porcelain in recognition of the services rendered by him. 

 to the Geological Survey of France. 



We are pleased to hear of the foundation of the Zoological 

 Society of Western Australia, with the object of establishing a 

 Zoological Garden at South Perth in that colony. Mr. E. A. 

 Le Souef has been appointed director of the new institution. 



It is announced that the Council of the Iron and Steel 

 Institute have accepted an invitation from the Association of 

 Swedish Ironmasters to hold the autumn meeting of the 

 Institute next year at Stockholm. The meeting will be held 

 in August, and, in view of the large quantities of Swedish iron 

 and ores consumed in this country, there is no doubt that it willt 

 prove a very popular meeting. Previous autumn meetings of 

 the Institute have been held at Belgium, France, Germany,. 

 Austria-Hungary, Spain, and the United States. 



