672 NATURE 
spondingly high. Round the upper portion of this 
pillar is a strong lattice work structure, capable of 
rotation round the pillar, and to this is fixed the ver- 
tical telescope with a second mirror. and the objective 
at its upper end, the lower end carrying the large 
spectroscope, the collimator of which is vertical. For 
different declinations of the object under investigation 
the vertical telescope can be moved round in azimuth. 
In the communication in question Dr. Schlesinger 
describes all the chief portions of the instruments in 
detail, and numerous reproductions accompany the 
text. The latter part of the paper contains an inves- 
tigation on the rotation of the sun by spectroscopic 
means made with the instrument described briefly 
above. Reference should be made to the paper itself 
formule derived for the solar rotation by the spectro- 
scopic method, may be here reproduced :— 
Fermala Equatorial 
Velocit 
3 2 km. 
Duner 14-81—4:2 sin*@ ... 2:09 
Halm 14°53—2°5 wee) | 205 
Adams ... att 14°54—3°5 ates 205 
Storey and Wilso 14-75 — 3:2 Se ge riote. 
Plaskett @: PG: 14:37—4:0 en meee 
De Lury ... 14:04 — 4:0 a RO 
Hubrecht Wr we 13:23 —3-2 saa) een E: SO 
Evershed and Royds ... 13-77 Pane Gey"! 
Schlesinger 14:17 —3°4 2-00 
It should be stated that Duner’s and Halm’s ob- 
servations were visual, and that Hubrecht found a 
difference of 0-8° between the coefficients of sin? for 
the two solar hemispheres and the value given above 
is the mean. Dr. Schlesinger is strongly of the 
opinion that the causes of the diversity of the results 
are due to systematic errors at the telescope and at 
the measuring machine. 
FLUCTUATIONS IN THE YIELD OF SEA 
FISHERIES,} 
Ose can be little doubt that this report by 
Dr. Hjort will mark an epoch in the history of 
scientific fishery investigations. If the arguments 
upon which its conclusions are based successfully 
withstand the test of criticism, there has been estab- 
lished a method of predicting the probable future 
course from year to year of some of our most im- 
portant fisheries, which should be of the utmost value 
both to those engaged practically in the fishing in- 
dustry and to those responsible for fishery administra- 
tion. 
The report is the result of many years of observa- 
tion, and although the lines upon which the work 
has proceeded, and the character of the results which 
were expected, have been described by Dr. Hjort and 
his fellow-workers from time to time, this is the first 
report in which the whole matter has been brought 
forward in a comprehensive way, and the first time 
that all the data upon which the conclusions are based 
have been available. It is now possible to form a 
judgment as to the value of the work already done 
and as to the promise which it holds out of still more 
useful results in the future. 
It is one of the most characteristic features of the 
great sea fisheries that they are subject to remark- 
able fluctuations from time to time. Sometimes these 
fluctuations are seasonal, sometimes annual, but more 
often, perhaps, we have a series of years of successful 
fishery, followed by another series of comparatively 
1 Fluctuations in the great fisheries of Northern Europe viewed in the 
light of biological research. By Johan Hjort. Con. perm. internat. Explor. 
Mer. Rapp. et proc. verb. XX. Copenhagen, r19rq. 
NO. 2339, VOL:"G3) 
[AUGUST °27, 1914 
lean years. These fluctuations are especially notice- 
able in the case of the fisheries for the so-called 
pelagic fish, such as the herring, mackerel, pilchard, 
and anchovy, and, to a less-marked degree, in the 
case of the cod and haddock. Dr. Hjort’s principal 
results refer to the herring, but a considerable amount 
of attention has also been given by him and his 
colleagues to the cod and haddock. 
The case of the herring is the most conclusive. 
The main evidence has been obtained by the deter- 
mination of the age of the fish from the markings on 
the scale. As in the case of many other fishes, there 
| is little or no growth of the fish during the winter, 
and the difference in growth between winter and 
| summer is clearly marked on the scale of the fish, 
for details, but the interesting table, showing the | 
the period of small winter growth being represented 
by a dark mark or ring. By counting the number of 
such rings the age of the fish can be determined, so 
that the year in which it was born becomes known. 
In a sample of the fish taken at any particular time 
it is therefore possible to determine in what propor- 
tions the different year classes are represented. 
This method of age analysis has now been applied 
to Norwegian herring for a series of years with 
somewhat remarkable results. It has been found 
during the period 1907 to 1914 that fish of the year 
class 1904, that is to say, fish born in the year 1904, 
have occupied a very prominent position throughout, 
at first forming a large proportion of the shoals of 
smaller herring (‘‘fat herring” as they are called in 
Norway, fish from 19-26 cm., still quite immature), 
and in later years being equally prominent amongst 
the larger fish (‘“‘large herring,” fish from 27-32 cm., 
and ‘‘spring herring,’’? the actually spawning’ fish). 
The following table shows the percentage of fish of 
the 1904 year class in the samples examined each 
year from 1907 to 1913 :— 
Per cent. 1904 in 1907 1908 1909 I9IO IQII I9I2 1913 
Among fat herring ... 51°3 3778) 116%9)) 4:5) (0) 0 fo) 
Among large herring 7°7 516 48°38 59°6 46°0 52°5 586 
Among spring herring 1°6 34°8 43°7 77°3 70°0 64°3 64°7 
The 1904 fish, therefore, formed more than 50 per 
cent. of the immature ‘‘ fat herring’’ in 1907, and oc- 
curred amongst this class of fish in diminishing propor- 
tion until 1910. Amongst the “large herring,’’ 51-6 
per cent. were 1904-spawned fish already in 1908, and 
fish of the same year class occurred in large propor- 
tions each year until 1913, when there were still 58-6 
per cent. Turning to the ‘“‘spring herring ’’—the 
large spawning fish—the 1904 group was represented 
each year by a larger percentage, until in 1Ig1o it 
constituted 77-3 per cent. of all the fish. Since that 
time the percentage has only slightly fallen off, being 
still 64-7 per cent. in 1913. In the last chapter of 
the report the figures for 1914 are given, the percent- 
ages of the different year groups amongst the spring 
fish being as follows (p. 219) :— 
Spring Fish, 1914. Total number of Herrings 
examined 2205. 
Age in Years... 4 5 6 7 8 9 
Year of Birth .. ... I910 1909 1908 1607 1906 1905 
Percentage of fish in 
each age group... 0'6. {312 OO eS 2 an ao mE 
Age in Years... aot) LO IT 12 1033 14 15 
Year of Birth ... 1904 1903 1902 I90I1 1900 1899 
Percentage of fish in 
eachsagelgnroupear..! 54:3 Tis I'5 12) + O}4 eons 
In the year 1914, therefore, we still have, in the 
samples examined, 54:3 per cent. of the fish derived 
from the spawning of the year 1904. It should be 
added that the 2,205 fish are the combined total of 
| eight samples taken at different points on the Nor- 
