SEPTEMBER 4, 1913] NATURE 5 
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The Spectra of Helium and Hydrogen. 
Tue spectra of helium and hydrogen have acquired 
considerable importance in view of the recent experi- 
-mental researches of Prof. Fowler and the theoretical 
investigations of Dr. Bohr. Before the appearance of 
Fowler’s investigation the only hydrogen series known 
terrestrially were the diffuse series, consisting of the 
He, HB, &c., lines, and the infra-red series predicted 
by Ritz, two members of which (18751-3 and 12817-6) 
were observed by Paschen. However, by passing a 
strong condensed discharge through mixtures of 
helium and hydrogen, Fowler was able to photograph 
four members of the principal series, the strongest 
line of which is at 4686. 
It should be noted that the 4686 line appeared on the 
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II. 
photograph of the spectrum of a helium tube, which 
had been taken at the Solar Physics Observatory at 
South Kensington several years ago. Sir Norman 
Lockyer and Baxandall in their paper pointed out that 
the terrestrial line was very probably identical in origin 
with the chromospheric line of nearly the same wave- 
length photographed Curing the eclipse of January, 
1898. They also noticed that the 4685-90 chromo- 
spheric line is of the same nature as the helium 
eclipse lines, being long and sharply defined. They 
concluded that the line is probably due to a gas, which 
is associated in some way with helium. The 4686 
line has also been observed in the spectra of stars of 
the fifth type, and in the spectra of certain nebule, 
and had been attributed to hydrogen in accordance 
with Rydberg’s calculations, which depend on the 
numerical relations existing between the different 
series. 
__ In addition to the series having the 4686 line as 
first member, Fowler was able to photograph three 
members of the sharp series, which are found in the 
spectrum of & Puppis, and three members of a new 
ultra-violet series, which he calls the second principal 
series of hydrogen. According to the theory put for- 
ward by Dr. Bohr, the two principal series _and the 
NO. 2288, VOL. 92] 
this cr eny other part cf Naturr. No notice is 
—4713 
— 4686 
— 3889 
sharp series are given by helium. Also it should be 
possible to obtain the diffuse series from helium con- 
taining no hydrogen when the sharp series appears. 
For some time I have been investigating the origin 
of the 4686 line, and the experiments already carried 
out support Bohr’s theory. The chief difficulty con- 
sisted in driving out hydrogen from the poles of the 
helium spectrum tube, but this was accomplished so 
far as spectroscopic evidence goes. No hydrogen 
could be detected in the bulbs and capillary when 
heavy discharges from a coil capable of giving a 
20-in. spark were passed through the tube. The 4686 
line was strong in the capillary and fairly strong in 
the bulbs. The pressure of helium employed in these 
experiments varied from about 0-25 mm. to 1 mm. 
The capillary, in addition to the helium spectrum and 
the 4686 line, showed impurity lines due to oxygen. 
Photographs I. and II. show the spectra obtained 
when a strong condensed discharge is passed through 
helium at pressures of t mm. and 0-3 mm. respectively. 
In the first photograph the 4686 line is of nearly 
the same intensity as the 4713 helium line, and the 
two are scarcely separated in the reproduction. The 
low-pressure photograph (Fig. 2) shows the 4686 line 
much stronger than the 4713 line. In 
both cases the hydrogen lines at 6563 
and 4861 are not seen. The 4686 line 
could not be obtained from an ordinary 
hydrogen tube, nor from a neon tube 
containing a small amount of hydrogen 
as impurity. A tube containing a mix- 
ture of hydrogen and purified argon 
was also prepared, but the line was not 
visible when heavy condensed discharges 
were passed through the mixture. 
E. J. Evans. 
The University, Manchester, 
August 11 
3889 
Coloured Organisms on Sea-Sand. 
A variED and interesting field of 
investigation awaits the microscopist 
who will make a detailed examination 
of the minute fauna and flora of ap- 
parently barren sands on the seashore. 
To-day, on landing at the island of 
Oronsay at low tide, the otherwise 
pure white sand was seen to be 
coloured pink in one area, for an 
extent of several yards, green a little further 
up the beach, and golden-brown in small patches 
here and there. On examining samples with the 
microscope the brown colour was found to be due 
to living diatoms (not dinoflagellates in this case), 
naviculoid forms like Caloneis; the pink is formed 
of amorphous masses of fine granules in a jelly loosely 
adhering to the sand-grains, and may perhaps prove 
to be bacteria in a zoogloea state, while the green is 
caused by patches of a very simple alga (? a Cocco- 
phycid) made up of groups of rounded green cells in a 
single layer on the sand-grains. I have kept samples 
of all the organisms and will submit them to a botanist 
for more precise identification. _No Amphidinium 
patches were present so far as I could see. The 
variety of organisms present in the one little bay, the 
extraordinary abundance in each patch, and the bright- 
ness of the colour produced on the white sand were 
very striking, and seemed worthy of note. 
The colour was not in any of these cases due to the 
sand-grains themselves, which are mostly clear quartz 
with, as usual, a few black specks and some white 
shell fragments. Nor was there apparently any fresh- 
water on the beach, and certainly not any sewage or 
other source of impurity. It is a lonely, sandy bay, 
