448 
in France. In 1892 a 36-inch glass was made for 
the Lick Observatory by Alvan Clark, and a 40-inch 
for the Yerkes Observatory in 1897. These large 
telescopes led to the discovery of new satellites, the 
accurate determination of the sizes of planets and 
satellites, but their main work—used visually—was 
the discovery and measurement of large numbers of 
double stars, leading to a very satisfactory knowledge 
of the masses of stars. Used with the spectroscope, 
they gave the velocities of stars to and from the 
earth, and enabled the velocity of the sun among the 
stars to be determined as 19 kilometres per second. 

NATURE 
| This result, in combination with measurements of 

[Marcu 31, 1923 
angular motions of stars, served to give the mean 
distances of stars. Large photographic refractors 
have made possible the measurement of the actual 
| distances of thousands of stars, leading to a much 
more complete view of the alge system. 
The discoveries made by the large 60-inch and 
too-inch reflectors of Mt. Wilson and the 72-inch of 
British Columbia were also detailed, culminatin; 
with the measurement of the size of the disc o 
Betelgeuse and of several other stars by the inter- 
ferometer as applied by Michelson, 
Irish Sea Plankton. 
IR WILLIAM HERDMAN, in an interesting 
paper recently issued, gives a sunymary of 
plankton researches in a single area extending over 
a period of fifteen years, and compares the results in 
each year in such a way that certain general facts 
are at once apparent. 
The object of the investigations was twofold: “ (1) 
To study the distribution of the plankton as a whole, 
and of its various constituents during the year; and 
(2) to arrive at some estimate of the representative 
value of the samples collected in the plankton nets.” 
The results show very clearly that the distribution 
of life in the sea is not uniform, but that the organisms 
appear in patches. Although this applies to a certain 
extent to all the plankton, it is especially the case 
with the copepods, which are frequently present in 
large swarms in one place, while possibly only a 
short distance away few or none occur. This natur- 
ally affects the distribution of other organisms feed- 
ing on the copepods, especially fishes, and is of 
fundamental importance. The diatoms were found 
to be more evenly distributed both vertically and 
horizontally during their maximum in the spring 
than at any other time. Comparing the records for 
the fifteen years (1907-21), there is always this spring 
maximum of phytoplankton (chiefly diatoms), which 
may range from March to June and reach to hundreds 
of millions in one haul, a dinoflagellate maximum, in 
much smaller numbers, coming on about a month 
later; and later still, a copepod maximum ranges 
from June to October. In late summer or autumn 
each group may have a second smaller maximum in 
the same order. 
That the bulk of the plankton consists of a small 
number of genera, chiefly diatoms and copepods (and 
only a few species of copepods), is well established, 
and these few form the chief food of most of the 
marine animals. So far as fishes are concerned, 
copepods are by far the most important food of the 
young stages, and also of the plankton-eating adults ; 
but as most copepods are predominantly diatom 
feeders the presence of diatoms is quite as important 
to the fish as to the copepod. With regard to the 
phytoplankton, however, Sir William Herdman ap- 
parently regards it as the direct food of many larval 
fishes, at any rate of the plaice in its infancy, which 
he has seen with its stomach full of diatoms. 
The diatom maximum occurs usually just before 
the time when most of the fish larve begin to be 
abundant, and the copepods follow. These plankton 
investigations are thus of great importance rela- 
tive to the food of fishes. 
Dr. Johan Hjort suggests that large mortality 
among the fish larva may occur because of the lack 
of suitable food at the time when they begin to feed. 
In the present plankton investigations, together with 
data gathered from experiments in the plaice hatch- 
ing at the Port Erin Biological Station, it is shown 
1“ Spolia Runiana. V. Some Results of Plankton Investigations in the 
Irish Sea,” by Sir William Herdman. Extracted from the Linnean Society’s 
Journal—Botany, vol. xlvi., July 1922. 
NO. 2787, VOL. 11T] 

that diatoms are abundant usually a short time 
before the very young plaice are set free; but in 
four out of thirteen years the diatoms were late, and 
in these years it is possible that the young fishes may 
not have found enough to eat. ‘‘ The evidence so 
far seems to show that larve set free as late as March 
20 are fairly sure of finding suitable food : but if they 
are hatched as early as February they run some chance 
of being starved.” j 
While discussing fully the phytoplankton in rela- 
tion to fish larve very little is said of the zooplankton 
other than copepods, and one would infer from the 
conclusions that it is only the diatoms which are of 
importance as young fish food in the spring. It is, 
however, probable that in spite of the fact that more 
diatoms than anything else are present, yet the zoo- 
plankton is really of more direct value as food for the 
larval and post-larval fishes: for example, cirripede 
nauplii and mollusc larve besides copepods, the latter, 
although not at their height in the spring, yet occurring 
in large numbers. 
Sunlight is shown to play a very important part 
in the growth of the plankton. In the daytime, how- 
ever, the largest hauls are usually not at the surface 
but at about five or ten fathoms, the depth varying 
with the meteorological conditions. It is regarded as 
probable that the spring phytoplankton maximum is 
due chiefly to the great increase of sunlight aided by 
the winter increase of carbon dioxide and other food 
matters. The rapid disappearance of the diatoms 
after the spring maximum is accompanied by a greater 
alkalinity of the water, and it is suggested that it 
may be due to the injurious effect of their own 
metabolism. May not the explanation lie partly in 
the fact that the diatoms are eaten by an enormous 
number of pelagic animals coming on just after the 
diatom maximum ? 
As to the representative value of the samples 
collected in the plankton nets, it is shown that 
variation in the composition of similar hauls is great. 
These differences show clearly that the life in the sea is 
not spread evenly either horizontally or vertically, but 
everywhere occurs irregularly. Simultaneous hauls of 
similar nets were usually different in quality even if 
alike in quantity, and the same applied to successive 
vertical hauls in which the amount of organisms was 
much the same in each haul but different in kind. 
In plankton investigations in which tow-nets are 
used, however carefully the experiments may be 
carried out, there is necessarily a great deal of in- 
accuracy, which is freely admitted and discussed. 
None of the numerical results can be absolutely exact, 
but when, by examining and recording these, certain 
phenomena are seen to repeat themselves year after 
year, we can at least feel sure that by making these 
careful quantitative experiments in connexion with 
numbers of hauls all carried out in an exactly similar _— 
way, we are approaching the solution of the general 
problems relative to the distribution of life in the sea. 
MWe 
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