Sept. 2, 1880J 



NATURE 



415 



while lithium gives single lioes, which, including the green line, 

 which they show really to belong to lithium, though it was 

 ascribed to cccsium by Thalen, also recur in a similar way. In 

 these three metals the law of recurrence seems to be the same, 

 but the wave-lengths show that the whole series are not simple 

 harmonics of one fundamental, although between some of the 

 terms very simple harmonic relations can be found. Between 

 the lines G and H are two triplets of iron lines, which, according 

 to Mr. Lockyer, do not belong to the same molecular grouping 

 as most of the other lines. In many photographs of the iron 

 spectrum these triplets have appeared almost alone. Also the 

 two triplets are not always in the same relation as to brightness, 

 the more refrangible being barely visible with the spark ; com- 

 bining this with Young's observations, in which some short weak 

 lines near G appear in the chromosphere 30 times, w hile one of 

 the lines of the less refrangible triplet only appears once, and 

 with the fact that in the solar spectrum the more refrangible triplet 

 is much the more prominent of the two, Mr. Lockyer is led to 

 the conclusion that these two triplets are again due to two dis- 

 tinct molecular groupings. 



There is one difficulty which must be taken account of in 

 connection with Mr. Lockyer's theory with regard to the produc- 

 tion of successive stages of dissociation by means at our command: 

 (l) by combustion of different substances ; (2) by an electric arc, 

 which will probably give different temperatures according as it 

 is produced by different dynamo-electric machines ; (3) by the 

 induction spark without ; and (4) with a condenser. 



At each stage of the process there must be a considerable 

 absorption of heat to produce the change of state, and our 

 supply of heat is limited in the electric arc because of the dis- 

 sociation of the conductors, and more limited still in quantity 

 in the electric spark or in the discharge through a vacuum 

 tube. Also we should expect a recombination of the dissociated 

 substances immediately after they have been first dissociated. 

 Hence it seems easier to suppose that at temperatures which we 

 can command on the earth, the dissociation of molecules by the 

 arc or the spark is accompanied by the formation of new com- 

 pounds, in the formation of which heat and light, and especially 

 chemical vibrations, would be again given out, thus giving rise 

 to new spectra, rather than to suppose that we can reach the 

 temperature necessary for successive stages of dissociation. 



To the lines C, F, the line near G, and // belonging to 

 hydrogen, which have a certain rhythmical character, Mr. 

 Lockyer adds D3 and Kirchhoff's line "1474," regarding "1474" 

 as belonging to the coolest or most complex form, rising to F 

 at a higher temperature, which is again subdivided into C and 

 G, using the spark \^ithout a condenser, which again gives // 

 with the spark and condenser, which is again split up and gives 

 D3, a more simple line than//, in the Chromosphere. Professors 

 Liveing and Dewar, on the other hand, trace a rhythmical 

 character or r.itio between three of the brightest lines of the 

 Chromosphere, two of which are lines "1474" and "f" of 

 Lorenzoni similar to the character of C, F, and h of hydrogen, 

 and also trace a similar relation between the chromospheric line 

 D3 and "1474" to the ratio of the wave-lengths of F and the 

 line near G. They infer the probability that these four lines are 

 due to the same at present unknown substance, as had been 

 suggested by Young with regard to two of them. The harmony 

 of this arrangement is somewhat disturbed by the fact that D3 

 lies on the wrong side of " 1474" to correspond with the line 

 near G of the hydrogen spectrum. 



If we inquire what our sun and the stars have to say to these 

 changes of spectra of the same substance at different tempera- 

 tures, Dr. Huggins gives us the answer. 



In the stars which give a very white light, such as Sirius er a 

 Lyr.-c, we have the lines G and h of hydrogen and also H, 

 w hich has been shown by Dr. Vogel to be coincident with a line 

 of hydrogen ; but the K line of calcium is weak in a Lyra:, and 

 does not appear in Sirius. In passing from the white or hottest 

 stars to the yellow stars like our sun, the typical lines diminish 

 in breadth and are better defined, and K becomes stronger 

 relatively to H, and other lines appear. In Arcturus we have 

 a star which is probably cooler than our sun, and in it the line 

 Iv is stronger in relation to II than it is in the solar spectrum, 

 both being very strong compared with their state in the solar 

 spectrum. 



Professors Liveing and Dewar find that K is more easily 

 reversed than H in the electric arc, which agrees with the idea 

 that this line is produced at a lower temperature than II. 



Besides the absence or weakness of K, the white stars have 



twelve strong lines winged at the edges, in which there are 

 three of hydrogen, viz. G, h, and H, and the remaining nine 

 form a group which are so related to one another that Dr. 

 Iluggins concludes they probably belong to one substance. 

 Three of these lines are said by Dr. Vogel to be lines of 

 hydrogen. Liveing and Dewar have made considerable pro- 

 gress in determining the conditions and the order of reversal of 

 the spectral lines of metallic vapours. They have adopted 

 methods w-hich allow them to observe through greater thick- 

 nesses of vapour than previous observers have generally em- 

 ployed. For lower temperatures tubes of iron or other material 

 placed vertically in a furnace were used, and the hot bottom of 

 the tube was the source of light, the absorption being produced 

 by vapours of metals dropped into the hot tube and filling it to 

 a greater or less height. By this means many of the more 

 volatile metals, such as sodium, thallium, iridium, cccsium, and 

 rubidium, magnesium, lithium, barium, strontium, and calcium, 

 each gave a reversal of its most characteristic line or pair of 

 lines, i.e. the red line of lithium, the violet lines of rubidium 

 and calcium, the blue line of strontium, the sharp green line of 

 barium (5535), and no other lines which can certainly be 

 ascribed to those metals in the elementary state. 



For higher temperatures tubes bored out in blocks of lime or 

 of gas carbon, and heated by the electric arc, were used. By 

 keeping up a supply of metal and in some cases assisting its 

 volatilisation by the admixture of a more volatile metal, such as 

 magnesium, and its reduction by some easily oxidisable metal, 

 such as aluminium, or by a current of coal gas or hydrogen, 

 they succeeded in maintaining a stream of vapour through the 

 tube so as to reverse a great many lines. In this way the 

 greater part of the bright lines of the metals of the alkalies and 

 alkaline earths were reversed, as well as some of the strongest 

 lines of manganese, alnminium, zinc, cadmium, silver, copper, 

 bismuth, and the two characteristic lines of iridium and of 

 gallium. By passing an iron wire into the arc through a per- 

 forated carbon electrode they succeeded in obtaining the rever- 

 sal of many of the lines of iron. In observing bright-line 

 spectra they have found that the arc produced by a De Meritens 

 machine arranged for high tenison gives, in an atmosphere of 

 hydrogen, the lines C and F, although the arc of a powerful 

 .Siemens machine does not bring them out, and they have 

 observed many metallic lines in the arc which had not been 

 ])reviously noticed. The temperature obtained by the De 

 Meritens machine is thus higher than that obtained in the 

 Siemens machine. 



From observations on w-eighed quantities of sodium, alone and 

 as an amalgam, introduced into a hot bottle of platinum fiUed 

 with nitrogen, of which the pressure was varied by an air-pump, 

 they conclude that the width of the sodium lines depends rather 

 on the thickness and temperature of the vapour than upon 

 the whole quantity of sodium present. Very minute quantities 

 diffused into the cool part of the tube gave a broad diffuse absorp- 

 tion, while a thin layer of compressed vapour in the hot part of 

 the tube give only narrow absorption lines. Professors Liveing 

 and Dewar have observed the reversal of some of the well-known 

 bands of the oxides and chlorides of the alkaline earth metals. 

 The lines produced by magnesium in hydrogen form a rhythmical 

 series extending all across the well-known B group, having a close 

 resemblance in general character to the series of lines produced 

 by an electric discharge in a vacuum tube of olefiant gas. 



The series appear:; at all temperatures except when a large 

 condenser is employed along with the induction coil, provided 

 hydrogen is present as well as magnesium, while they disappear 

 when hydrogen is excluded, and never appear in dry nitrogen or 

 carbonic oxide. 



From their experiments on carbon spectra they conclude with 

 Angstrom and Thak-n that certain of the so-called "carbon 

 bands " are due to some compound of carbon with hydrogen, 

 probably acetylene, and that certain others are due to a compound 

 of carbon with nitrogen, probably cyanogen. 



They describe some ultraviolet bands : one of them coincides 

 w ith the shaded band P of the solar spectrum which accompanies 

 the other violet bands in the flame of cyanogen as well as in the 

 arc and spark between carbon electrodes in the nitrogen. All 

 the bands which they ascribe to a compound of carbon and 

 nitrogen disappear when the discharge is taken in a non-nitro- 

 genous gas, and they reappear on the introduction of a minute 

 quantity of nitrogen. 



They appear in the flame of hydrocyanic acid, or of cyanogen, 

 even when cooled down as much as possible as shown by Watts, 



