Page:Proceedings of the Royal Society of London Vol 69.djvu/143

Rh The spectrum has undergone great modification since the last photo- graphs were taken at Kensington in March and April. The lines are about the same in number and position, but their nature and relative intensities have vastly changed. In the latter part of March and the early part of April the lines were generally broad and ill-defined. They are now narrower, and with better defined edges. The greatest change noticeable in the spectrum is with respect to the relative weakening of the hydrogen lines generally and the alteration in relative intensity amongst some of them. In the earlier photographs the hydrogen lines were very prominent, and the individual members of the series gradually weakened as the ultra-violet part of the spectrum was approached. In the latest photographs they appear of quite secondary importance. H/2, Hy, and H8 are all present, but occur only as comparatively weak lines, especially the latter two. With regard to He, apparently the only other hydrogen line shown, the case is different. The line at or near the position of He is now about the second strongest line in the whole photographic spectrum, and many times stronger than either H6\ Hy, or H/3. With this fact in view, it may be suggested that this strong line is possibly not wholly due to hydrogen, but is mainly a new line of unknown origin, which happens to fall exactly on, or very near to, the position of He. The line appear.-* to be of much the same nature as the stronger .adjacent line at A 3868. The following table gives the wave-lengths and intensities of the lines visible in the photographs :

AA.

Int. (max. = 10).

Remarks.

3SC8 3970

10

8

Strong line in spectrum of planetary nebulae. Probably not wholly due to hydrogen (Ut)> intensity

abnormal.

4102

2

US.

4341

2

H 7.

4364

7

4471

1

Helium.

4G36

3

4684

2

Probably identical with 4687 of Puppis and

Orion

stars.

4720

6

4808

<1

4862

3

H/3. 4959

2

Apparently identical

with second nebula line.

5007

strongest

In addition to the lines in the above table, six of the photographs, including that of August 26, give indications of the presence of a line in the extreme ultra-violet. Its wave-length could not be obtained