Oct, 17, 1878J 



NATURE 



of Thalen, Huggins, and PlUcker were given in wave-leno-ths 

 only, fractions being omitted altogether. Error amounting to 

 half a wavelength could therefore exist in the position of a line 

 according as it fell on one side or the other of a figure on the 

 scale expressing a wave-length. In the values given to the air- 

 lines by Angstrom in his chart, this difficulty did not exist ; I 

 therefore attempted the use of Angstrom's values, employino- the 

 work of Huggins and Pliicker, to separate as far as po-^sibll the 

 oxygen from the nitrogen lines. This operation was, however 

 quickly discarded; because of the great differences existin<^ 

 between these authorities regarding the wave-lengths of a 

 number of oxygen and air -lines. To obviate this trouble I 

 made photographic measurements of the lines of the electric 

 spectrum of oxygen by the method detailed below 



The apparatus employed consisted of a spectroscope with two 

 iiint glass prisms of 60°, adjusted to the minimum deviation of 

 p. Collimator and telescope objectives, achromatics of ten 

 inches focus. This was used to make photographs of the spectra 

 given by the condensed electric spark in oxygen, in air, and in 

 nitrogen. When so employed the eye-piece of the telescope 

 was removed, and a camera placed in its stead. The slit was 

 sometimes made as narrow as was possible. The induction-coil 

 was one of Ritchie s, giving a ten-inch spark, and havin<r a 

 hammer current-breaker driven by clock-work. The battery 

 was three two-gallon bichromate cells, the elements were lar<re, 

 but just touched the fluid when the battery was in operation. 

 The large mass of fluid in proportion to the immei^ed area 



^,,™ tT^ T^^^ ^° l"PP'>^ ^ ^'^^y "'"for"» primary 

 cm rent. The condenser on the secondary current consisted of 

 ten glass plates, each having a tin-foil coating of thirty- six 

 square inches. One or more of these plates could be thrown 



J!!,mhlr^ nf'""^' ^^ °'f '^"/^ l^^"^''"'^- ^y t^i^ arrangement a 

 number of photographs of the electric spark, between plati- 

 num and iron points, in atmospheres of oxygen, and of oxygen 

 and nitrogen, were made. The positions of the iron and 

 oxygen lines in these were measured, as in the solar photo- 

 graphs, by projection under a suitable magnifying power 



655 



The centre of each line was the portion from which measures 

 were taken in all cases. The wave-lengths of the oxygen-hS 



to A44I4 75 was based on the iron lines of the same spectnim 

 aSou ZT^r^"" ^-on}^^^^ in this extent of the specS^am, or 

 about one to every eleven wave-lengths were used. The 

 values assigned to the iron lines were those obtained in my 

 chart of the solar spectrum. By this method of measurement 

 error, arising from maladjustment of two spectra were avoided 

 fTs \^^%'^^ ' K,''^^?^ the iron lines did not photograph'; 

 I ^^as therefore obliged to construct this portion of the curve 

 from the wave-lengths of oxygen and air-lines already given 

 ZZlT'^l authorities, selecting those values in which "they 

 rn%f V "^^"^ ^"^ 441475 the results are therefore accu 



^^i^l -f '■°"' 441475 to 4705, though they are approximate, the 

 error, if any exists, must be very small. The measurements to 

 fractions of a wave-length were obtained by constructing the 

 curve on a scale of sufiicient magnitude. 



In illustration of the great nSmber of lines presented by my 

 chart of the solar spectrum, as compared with that of Angstrom 

 B^^l '""^^ '^''*'°'' extending from 4062 to 4080, "within 

 which the oxygen group 4069-8o-4O72-ic— and 4075-50 fall= 

 On the upper part of the diagram the symbols of the elements 

 are placed, to which, according to Angstrom, corresponding lines 

 are found m the solar spectrum. On the first space below the 

 line 13 the scale of wave-lengths, each wave-length being five 

 milhmetres in extent. In the second space the lines of An<.- 

 strom s chart are given. In the third space the lines measur^ 

 on the photographs, the vertical portion of each symbol <nwm<y 

 he position, and the horizontal portion the width, and also 

 the darkness on an arbitrary scale of one to ten. The darkest 

 lines encroach most on the vertical portion of the symbol. 

 Ihe value 10 is expressed in the symbol of the Mn Fe line 

 4063, and the value i in that of the line 4068-05. Other 

 features of the lines are shown by the manner in which the 

 upper part of each of these symbols is drawn. Beneath the 

 spectrum-Iines the scale is repeated, and the position of the 



Mn 



Ca 



Fe 



Mn 



Fe 



11 I 1 ' t' I IT T 



m^ii 



J ! L_JL 



n^^TTTTf 



' i I r 



jit 



oxygen lines indicated. In addition to the lines already men- 

 tioned as being in Angstrom's chart, lines of the followino' 

 elements appear in this space, viz., Fe 4063, Pb 4066, Sr 

 4078, Bi 4080. The correspondence between these values 'and 

 the wave-lengths of the lines in the photographic spectrum is 

 as close as could be expected, seeing that the authorities do 

 not give fractions of wave-lengths. The Te line is represented 

 m the spectrum by the Mn Fe line 4063, the Pb line bv 

 the spectrum line 4065-7, the Sr line by the line 4077-Q, and 

 the Bi line by the line 4079-8, i- // y, c<nu 



Inspection of the diagram also shows that, while the Mn Fe 

 4063 lines are coincident in both charts, the Fe line 4071 

 of Angstrom reads 4071-25 in the photographic chart, and the 

 unassigned line 4076-25 of Angstrom reads about 4076-20, in 

 my chart the two lines being nearly coincident. In the photo- 

 graphic chart the relations of the lines to each other as reo^ards 

 position are accurately presented, and where these differences 

 occur the positions given in the photographic chart must be 

 correct. The total number of lines in the two charts is also 

 worthy of notice. ^ In the eighteen wave-lengths represented 

 in the diagram Angstrom gives six lines, while the photo- 

 graphic chart gives twenty-four. Of Angstrom's lines five are 

 assigned to different metals, if we give the line 4066-25 to Pb 

 and one is unassigned In the photographic chart these lines 

 -?!. f^P^f ' """^ '" ^^^i^xoxi the lines of Bi and Sr, together 

 with the three oxygen lines. Out of the twenty-four linesTen 

 are assigned to various elements, leaving fourteen to be ac- 

 counted for, and many of these are moderately stron- lines 

 The oxygen lines represented in the diagram are amon- the 

 strongest in the electnc spectrum of oxygen, yet the equiva- 

 ent hnesm^e solar spectrum are faint when compared with 

 the Imes of Ca and Fe. This would seem to indicate a low 



absorbing power in the gaseous non-metallic elements, as com- 

 pared with the same power in the case of metals in the vapour- 

 ou3_ state. The existence of a difference like this would ex- 

 plain why it is that many of the Hues in the solar spectrum 

 which represent oxygen have been overlooked. Some of these 

 lines have, however, been observed, Angstrom himself givin-r 

 m his chart a number of lines not assigned by him nor anv 

 one e se to other elements, which are very nearly coincident 

 with the oxygen lines, as determined by the photographic 

 method, as will be seen m the table at the close of this article 



As It IS not possible in the space to which we are limited, 

 to give diagrams of all the portions of the solar spectrum which 

 contain oxygen hnes, we present in the foUowing table the 

 positions m that spectrum of all the oxygen lines that were 

 obtained in the photographs of the electric spark in that gas 

 Ihe first column contains the wave-lengths of certain lines in 

 the chart made from photographs of the solar spectrum ; the 

 second the wave-lengths of the lines of the condensed electric 

 spark in oxygen ; the third Pliicker's lines of oxygen, which 

 are much m.ore numerous than those of Hucrgin^, which are 

 presented in the fourth column, while the fifth column gives 

 the lines of Angstrom's air spectrum, which may be credited 

 to oxygen. The term free in the first column is used to indi- 

 cate the fact that no element has heretofore been found to 

 give a line within two or three tenths of a wave-Ienoth of that 

 position. It is therefore free to be assigned as an oxygen line 

 Ihe chemical symbols on the other lines show that the element 

 indicated has been assigned to that line, and shares it with 

 oxygen. The number of lines of greater wave-length than 

 3961-60, which are free from other elements, and which are 

 assignable to oxygen, is good evidence of its presmce in the 

 solar envelopes. 



