266 
ASTRONOMY: IV. H. WRIGHT 
the other predominating calcium phosphate with much organic matter. 
The two groups, although they may be alike structurally, are physio- 
logically quite dissimilar, the chemical reactions involved in building 
the shells being of two different orders. Such a distinction ought to be 
significant to biologists, and it is for them to determine what it means. 
Geologically, however, we can see that the phosphatic brachiopods have 
probably played some part in the formation of phosphatic sediments, 
a function which is shared by vertebrate animals and some crustaceans. 
' Published by permission of the Director of the U. S. Geological Survey. 
2 Sharpies, S. P., Amer. J. Set., ser. 3, 1, 168 (1871). 
3 Kunckell, F., /. prakt. Chem., ser. 2, 59, 102 (1899). 
* Schmelck, L., Norske Nordhavs Expedition, No. 28, p. 129 (1901). 
6 Logan, W. E. and Hunt, T. S., Amer. J. ScL, ser. 2, 17, 237 (1854). 
emiger. A., /. prakt. Chem., 102, 418 (1867). 
' Cloez, S., Jahrber. Chem., 1859, p. 642. From Vlnstitut, 1859, p. 240. 
ON THE OCCURRENCE OF THE LINE 4686 A AND THE RE- 
LATED SERIES OF LINES IN THE SPECTRA OF 
THE PLANETARY NEBULAE 
By W. H. Wright 
LICK OBSERVATORY. UNIVERSITY OF CALIFORNIA 
Read before the Academy, December 9. 1914. Received. March 31.1915 
The line 4686 A and the related series of lines known as the ^ Puppis 
series, or 'sharp series' of hydrogen, were first observed in the spectra 
of the heavenly bodies. In 1912 Fowler succeeded in exciting them in 
a laboratory source. ^ More recently they have played an important 
role in certain theories of the constitution of the atom.^ 
The Unes in question exist in the spectra of the planetary nebulae, 
and a number of facts concerning their occurrence have been brought 
out in the course of an investigation, now being undertaken, of these 
spectra. This study, while not yet complete, has led to some tentative 
generalizations on the behavior of certain of the nebular lines, prominent 
among them the one at 4686, and it may add to the significance of some 
of the observations of this line if a brief account is given of these. In 
what follows I shall attempt to state in general terms what appear to 
me to be the most significant facts gathered from an examination of 
about a dozen planetary nebulae, and shall make only occasional refer- 
ences to individual objects. A detailed account of all of the observations 
will appear on the completion of the work. The conclusions arrived at 
here are, of course, subject to revision in the light of additional data. 
