654 



NATURE 



[Oct. 17, 1873 



during the last few years have been greatly impeded by the 

 restricted nature of the firmans granted, and constant disputes 

 were arising as to the area over which the firman extended. Mr. 

 Rassam has succeeded in obtaining a series of sufficiently open 

 permits to enable the new expedition to assume the nature of 

 a roving exploring party. The new firman includes the whole 

 of Mesopotamia, embracing the region around Mosul — that is, 

 the sites of Nineveh, Kalakh, and the ancient city of Assur, 

 the site of which is marked by the mounds of Kileh Shergat. 

 A special firman has been obtained to enable Mr. Rassam to 

 commence explorations in a hitherto untouched field — the dis. 

 tricts of North-Eastern Syria. This region, the country which 

 once formed the seat of the powerful Hittite kingdom, having 

 for its capital the city of Carchemish, is as yet a terra incognita 

 to explorers, and as its annals when discovered will form an im- 

 portant link in the chain of history which binds Assyria to the 

 West, great results may be expected from Mr. Rassam's explo- 

 rations in this district. 



We have on our table the following books :—" Pleasant 

 Ways in Science," R. A. Proctor (Chatto and Windus) ; 

 " Ancient History from the Monuments of Sinai," S. H. Palmer 

 (S.P.C.K.); "Crystallography," H. P. Gurney (S.P.C.K.); 

 " Bluthendiagramma," ist and 2nd Parts, Dr. A. W. Eichler 

 (Engelmann) ; " Studies from the Physiological Laboratory of 

 University of Cambridge" (University Press). — London Science 

 Class-Books (Longmans): — "Botany, Morphology, and Phy- 

 siology," W. R. McNab ; " Botany : Classification of Plants," 

 W, R. McNab; "Hydrostatics and Pneumatics," P. Magnus ; 

 " Invertebrata and Vertebrata," Prof. Macalister; "Motion 

 of the Moon," Dr. S. Newcomb (Washington); "Physical, 

 Geological, and Geographical Map of Great Britain," Prof. 

 Ramsay (Standford) ; " Meteorology of the Bombay Presi- 

 dency," Charles Chambers ; " Karl Ernst von Baer," Dr. Stieda ; 

 "Karl Friedrich Gauss, Hauptmann (E. J. Brill) ; "Report on 

 Iron and Steel as Manufactured by Messrs. Jones and Laugh- 

 lins," R. H. Thurston ; "On the Equilibrium of Heterogeneous 

 Substances," Parts I and 2, J. W. Gibbs ; "Skizzen aus 

 West Afrika," Oskar Lenz (A. Hofmann) ; "Les Produits de 

 la Nature," A. J. C. Geertz (C. Levy); "La Prevision du 

 Temps," W. de Fonvielle. 



The additions to the Zoological Society's Gardens during the 

 past week include a Cross Fox [Caiiis fulvus) from Colorado, 

 presented by Mr. Wilfred G. Marshall; a Common Otter (Ltitra 

 vulgaris), European, presented by Mr. W. H. Baylis ; a Brown 

 Mynah ^Acridvtheres fuscus), a Pied Mynah {Sternopastor contra) 

 from India, an Indranee Owl {Syrniiwi indrance) from Ceylon, 

 presented by Capt. J. Murray ; four Egyptian Geese {Chenalopcx 

 ixgyptiaca) from the Cape of Good Hope, presented by Mr. 

 Justice Denyssen ; two Leopard Tortoises ( Testudo pardalis) 

 from the Cape of Good Hope, presented by the Rev. G. H. R. 

 Fisk, C.M.Z.S. ; a Collared Peccary {Dicotyles tajacu) from 

 South America, deposited ; a Red-Sided Eclectus {Eclectus 

 polychlorus) from Malacca, a Black-Footed Penguin (Spheniscus 

 dcmersus) from the Cape of Good Hope, four Chinese Turtle- 

 Doves ( Turinr chinensis) from China, purchased ; a Hybrid 

 Mandrill Monkey (between C, mormon ? and AI. cynomolgiis 6 ), 

 an Indian Muntjac {Cervulus muntjac), born in the Gardens. 



ON THE PRESENCE OF DARK LINES IN 

 THE SOLAR SPECTRUM WHICH CORRE- 

 SPOND CLOSELY TO THE LINES OF THE 

 SPECTRUM OF OXYGEN"- 

 'T^HE measurement of the wave-lengths of the dark lines of 

 the solar spectrum obtained by photographs, and the cdu- 

 struction of a chart of the same, has for many years occupied 

 ' By John Christopher Draper, M.D., LI,.D., Professor of Natural His- 

 tory in the College of the City of New York. From the American Journal 

 f ^r October. 



my leisure time. As a result of the investigations connected 

 with this work, I have arrived at the belief that oxygen as well 

 as other non-metallic gaseous elements are represented in the 

 SDlar spectrum by dark lines in the same manner as metallic 

 substances. The lines in the case of oxygen are, however, very 

 faint when compared with those produced by metals in the 

 vaporous state. 



The apparatus employed in these investigations may be briefly 

 described as follows : ist, a spectroscope for photographing the 

 normal solar spectrum. As my purpose was to obtain photo- 

 graphs in which the positions of the lines should be as true as 

 possible, I resorted entirely to the process by reflection, and at 

 no time did the solar rays pass through glass ; all error that might 

 arise during refraction ^^■as thus avoided. The mirrors of the 

 heliostat were of flat glass silvered, the silver-surface being 

 polished served as the reflector. The surface of the concave- 

 mirror employed to bring the image of the slit to a focus, was 

 also silvered and polished. Gratings of 4,800 and 9,600 lines to 

 the English inch, ruled on glass by a machine constructed by 

 myself and by my assistant Mr. Sickels, and also an admirable 

 one of 17,280 lines to the inch, for -which I am indebted to Mr. 

 Rutherfiurd, were used. These were silvered with a thin coating, 

 and the unpolished silver surface employed to give spectra by 

 reflection. With the 4,800 line gratings the photographs were 

 in the ist and 3rd orders ; with these of 9,600 lines in the 3rd 

 order, and with 17,280 in the ist and 2nd orders. The accuracy 

 of the gratings was tested with satisfactory results by taking 

 photographs in equivalent orders of spectra on each side of the 

 normal. The photographs for the determination of the wave- 

 lengths of the solar spectrum were in sections of eighty to one 

 hundred and fifty wave-lengths. The gratings were adjusted to 

 the line of no deviation for the centre of each section of the 

 spectrum, as it was photographed. 



The wave-lengths of the lines of the spectrum were carefully 

 measured on the original photographs, by projecting them upon 

 a scale of wave-lengths, each wave-length being five millimetres 

 in extent. The scale was drawn upon slips of paper, which had 

 been glued to strips of well-seasoned pine wood cut with the 

 grain. The lantern used for projection was that described in 

 this journal for April, 1878. The distance of the lantern from 

 the scale, and the consequent magnifying power, was so adjusted 

 as to make the leading lines of the photograph coincide with the 

 same lines of Angstrom, drawn in their proper position below 

 the scale as is shown in the diagram given later on. Thus the 

 positions of the lines in each section of one hundred or more 

 wave-lengths were all made visible at once, and the errors in 

 Angstrom's chart corrected. From 4045 to o in the ultra-violet 

 the leading lines of Cornu were employed. Among the advan- 

 tages presented by this method of studying and measuring the 

 lines of the spectrum we may mention the opportunity offered 

 for several persons to inspect at the same time the details of the 

 section under examination, and submit them to intelligent dis- 

 cussion. To this we may add the facilities offered for comparing 

 many photographs with each other by marking below the scale 

 the peculiarities of one, and then projecting the others in order 

 upon the marks made. In this way the effects of duration of 

 exposure and manner of development of the image, together with 

 the variation in the size of the slit and focal distance may be 

 investigated, and their action on the details of the picture deter- 

 mined. Pictures may even be placed face to face, one a little 

 above the other, and examined in that position by projection. 

 From the measures thus obtained a chart of the spectrum was 

 constructed, which extended from E in the green to P in the 

 ultra-violet. The values assigned to the wave lengths in this 

 chart are those of Angstrom, and it is my purpose to present the 

 positions and characters of certain of these lines in this communi- 

 cation. 



The great increase in the number of lines in the chart made 

 from photographs by Mr. Rutherfurd's grating, compared with 

 that of Angstrom, led me to collect all the measurements of 

 spectrum lines of elements that I could find, for the purpose of 

 determining the character of the newly-measured lines. On 

 comparing the lines of the spectra of oxygen, nitrogen, and air, 

 as given in Watt's index of spectra, from the researches of 

 Thalen, Huggins, and Pliicker, 1 was struck with the number of 

 approximate coincidences between the wave-lengths of oxygen 

 lines and those of dark lines in my map. Attempting to make 

 a close comparison of the oxygen with the solar lines I was 

 confronted by the following difficulties, viz. : the measurements 



