2 70 



NATURE 



\_yuly \, 187S 



1. The wide part of a Pliicker tube generally shines with a 

 faint yellow light. When looked at by means of a prism the 

 spectrum is perfectly continuous. 



2. If a spark of an ordinary Ruhmkorff coil is taken in 

 oxygen at atmospheric pressure, one of the line spectra generally 

 appears, but when the break is put out of adjustment so as to 

 weaken the spark, the lines disappear and are replaced by a 

 continuous spectrum which has its maximum of intensity in the 

 greenish-yellow, and gradually fades away towards both ends of 

 the spectrum. 



3. Becquerel mentions an observation according to which 

 the point of the oxy-hydrogen flame takes a yellow colour when 

 an excels of oxygen is present. The description of the some- 

 what characteristic colour which Becquerel gives coincides 

 exactly with the colour of the spark in oxygen, when it shows 

 the continuous spectrum. According to Pliicker an excess of 

 hydrogen shows the hydrogen lines, and it is therefore reason- 

 able to suppose that in Becquerel's experiment the oxygen was 

 sufficiently heated up to become luminous. 



The continuous spectrum must not be confounded with the 

 continuous spectrum, which under high pressure forms the 

 background to the line spectrum. 



The Elementary Line Spectrum, — This is the spectrum which 

 is seen when a strong spark passes through oxygen at the 

 atmospheric pressure. It can be seen at all pressures when a 

 jar and air break are introduced into the circuit. 



The Compound Line Spectrum. — Pliicker, in his first investiga- 

 tion of oxygen, says it consists of four lines, one in the red, two 

 in the green, and one in the blue. In his later drawing of the 

 spectrum of oxygen, he gives a great number of lines of which 

 these four form a part. Wiillner says that the four lines in 

 question are always the first to appear in oxygen tubes. Thalen 

 and Angstrom do not give these lines ; Huggins does not give 

 them ; Salet does not give them. Pliicker and Wiillner are the 

 only observers who experimented under the circumstances under 

 which the lines appear. They come out equally well whatever 

 way the oxygen is prepared, whatever the nature of the elec- 

 trode, and I have seen them under the large glass receiver already 

 mentioned. The following is the appearance of the spectrum 

 of oxygen as it undergoes gradual exhaustion. 



When the pressure is sufficiently diminished to allow the spark 

 to pass, it shows a yellow colour and the spectrum is perfectly 

 continuous. Almost immediately, however, the four lines are 

 seen in the capillary part of the tube above the continuous spec- 

 trum. The continuous spectrum in the wide part is stronger than 

 in the narrow part. The four lines seem to have taken away 

 part of the energy of the continuous spectrum. As the exhaustion 

 proceeds, the spark spreads out in the wide part, and the con- 

 tinuous spectrum is therefore diminished and becomes less intense 

 than in the capillary part ; but it gradually loses in intensity 

 also in the narrow part, until the four lines stand out on a 

 perfectly black background. If under these circumstances the 

 jar and air break are inserted in the circuit, everything will 

 disappear and the elementary line-spectrum will come out. We 

 have here as complete a transformation as from the band- 

 spectrum of nitrogen to the line-spectrum of nitrogen taking 

 place under precisely the same circumstances ; and it is there- 

 fore not unlikely that the two phenomena are due to the same 

 cause. There are two reasons why the existence of the com- 

 pound line-spectrum of oxygen as a separate spectrum may have 

 escaped previous observers. There is a blue line in the elemen- 

 tary line spectrum which is nearly coincident with the blue line 

 of the compound line spectrum. It requires considerable disper- 

 sion to notice the difference ; the complete disappearance of the 

 compound line-spectrum has therefore escaped notice. The two 

 green lines and the red line of the compound spectrum widen 

 easily at higher pressure and as has been remarked by Wiillner, 

 even fuse together to a continuous spectrum. If the experiment is 

 therefore made at a pressure at which oxygen has a continuous 

 back -ground, the disappearance of these lines might be taken for 

 their widening and fusing together. No such mistake is possible 

 when the vacuum is good. I have not been able to determine with 

 certainty whether the red line seen at atmospheric pressure is a 

 remnant of the compound line-spectrum, or whether it is a line 

 of the elementary line-spectrum closely coincident. I am in- 

 clined to the former view, although it often seemed as if the line 

 seen at atmospheric pressure was less refrangible than the red 

 line of the compound line-spectrum. I have drawn attention in 

 a letter to Nature (vol. xvii. p. 148), to the fact that the 

 compound line spectrum of oxygen seems to be reversed in the 



sun. I have no further information to add on that point, and 

 the wave-length of the lines will be found in that letter. 



The Spectrum of the Negative Pole. — This spectrum has first 

 been correctly described by Wiillner. It consists of five bands, 

 one of which is too weak to be measured. Careful measure- 

 ments of the bands have been taken. With regard to the ex- 

 planation of the separate spectra found at the negative pole in 

 nearly all gases, I incline to the view that they are due to sepa- 

 rate molecular compounds which are formed at the pole. The 

 following experiments seem to support that view. When the 

 pressure is very small the spectrum of the negative pole extends 

 throughout that half of the tube which incloses the negative 

 pole, and which I shall call the negative half. If the current 

 bo suddenly reversed the spectrum of the negative pole will still 

 be seen at first, in that part which was the negative half and now 

 is the positive half of the tube ; but it will gradually disappear 

 and a permanent state will be established, in which the spectrum 

 of the negative pole is, as before, only seen in the negative half. 

 That it is the reversal and not the interruption of the current 

 which produces the result is easily proved by interrupting the 

 current and at once closing it again the same way, when no dif- 

 ference will be seen. If, however, the current be left inter- 

 rupted for some time, say one minute, so that any compounds 

 which may have been formed in the negative half may diffuse 

 into the other half, and if then the current is closed, either the 

 same or the opposite way, the negative spectrum will be seen at 

 first throughout the tube, but gradually disappear in the positive 

 half. 



If the current be rapidly reversed in succession, after a little 

 while, when the effect of the first reversal has disappeared, the 

 permanent state will always be established at once, and the 

 spectrum of the negative pole will appear only in the negative 

 half. 



If after the last experiment the current be interrupted for 

 some time and then closed, the spectrum of the negative pole 

 will at first be seen throughout the tube, and gradually disappear 

 in the positive half. 



It is not quite easy to see the explanation of the last two 

 experiments. 



The experiments were all made in the Cavendish Laboratory, 

 Cambridge, and I am much obliged to Prof. Clerk Maxwell for 

 the kindness with which he has placed the resources of the 

 Laboratory at my disposal. 



Linnean Society, May 24. — Annual General Meeting. — 

 Prof. AUman, F.R.S., president, in the chair. — The anniver- 

 sary address of the president dealt with a rhumi of the principal 

 recent discoveries in the anatomy and development of the Poly- 

 zoa, and of the resulting important features in their systematic 

 grouping. Much had been due to the labours of Busk and 

 Nitsche. It was maintained that investigations were mainly in 

 favour of the so-called ' ' brown bodies " being merely the re- 

 siduum of degraded and withered polypides, and that they have 

 no real morphological or physiological importance. He coin- 

 cided with the views of Nitsche, Joliet, and Busk, that the 

 supposed "colonial nervous system" is but an irregular plexus 

 of cellular and protoplasmic cords and filaments derived from 

 the walls of the zooecium or polypide cell, and not a true nervous 

 system. Joliet's idea of its being the origin of new polypide 

 buds and of certain minute free corpuscles found in the zooecium 

 is, however, too exclusive. Cyphonantes is a singular little free- 

 swimming marine creature, of pyramidal form, the soft body of 

 which is contained within a bivalve shell. Schneider has re- 

 garded it as a larval Polyozoon, and announced the startling 

 fact that before its transformation into the adult it becomes 

 totally disorganised and reduced to a homogeneous protoplasmic 

 mass, though previously its structure had been complex. There- 

 after arises a new polypide, and the whole is metamorphosed into 

 the adult form. Strange as this history may seem, it has 

 been confirmed by the researches of Nitsche and Joliet. 

 Finally, the question of "individuality," or the relation to the 

 polyzoal colony was taken up by the president, and the following 

 opinion enunciated — that the zooecium or cell in which the 

 polypide is lodged must be regarded as having a zooidal indi- 

 viduality independently of the polypide, which has a zooidal 

 individuality of its own, and that the two thus form a compound 

 element which becomes associated with similar ones in order to 

 form the colony. This compound element is thus composed of 

 two zooidal individuals — zooecium and polypide; on the zooe- 

 cium devolving the functions of sexual and nonsexual repro- 

 duction, and on the polypide that of nutrition.— Prof. Allman 



