682 

pany has now ceased to exist and the results of the 
experiments are published. There is very little good 
trawling ground off the coast. of Ceylon on account 
of the extensive areas of bottom covered by corals, 
etc. Off Cape Comorin, to the west, south, and 
east, an area of no less than 4000 square miles 
within the 1oo-fathom line was investigated. All of 
this was good trawling ground. Two tons of fish 
could be obtained per day’s working. The other 
paper discusses the irregularly cyclic nature of the 
Ceylon and Indian pearl fisheries. It is well known 
that there are periods of productive years, two to 
six in duration. These are followed by periods up 
to twenty-seven years in duration during which the 
fishery fails absolutely. The cause of the sterility is 
the destruction of the growing pearl oysters by, pre- 
datory fishes. An abundant deposit of oyster spat 
is soon followed by a great increase in oyster-feeding 
fish, and after a year or two the latter gain the 
ascendancy. The grounds then become almost abso- 
lutely denuded of oysters. Afterwards they are 
again planted with spat from irregularly distributed 
reproducing oysters, it may be at very considerable 
distances away. The distribution of spat on suitable 
grounds depends on a number of conditions, and it 
is relatively seldom that all of these are satisfied at 
the same time. The barren periods are therefore of 
much longer duration than the fertile ones. Only 
by artificial culture of the pearls can a permanent 
fishery be expected, since it is apparently hopeless 
to attempt to counteract the destructive action of the 
predatory fishes. 
OrniTHOLOGISTS will be glad to know that, in the 
Scottish Naturalist for August, Mr. John S. Tulloch 
makes a brief announcement of the fact that the 
gannet (Sula bassana) is extending its breeding range, 
four nests having been found on the Noup of Noss, 
Bressay. This record apart, only fifteen breeding 
stations of this bird are known, and of these nine are 
British. |The only English station, Lundy Island, 
has of late years been forsaken owing to the merciless 
persecuticn to which the birds were subjected. Wales 
has one station, Grassholme, off Pembrokeshire ; 
Ireland two, the Little Skelling, Co. Kerry, and the 
Bull, off Co. Cork. Scotland has five stations, all, 
save the Bass, on the west coast. 
it is to be noted, are islands, the gannet nowhere 
ever breeding on the mainland. 
Mr. J. H. Gurney and Miss E. L. Turner contri- 
bute some extremely interesting ‘‘ Notes on a Long- 
eared Owl Nesting on the Ground in Norfolk” to 
the British Birds Magazine for August. Inasmuch 
as there were suitable trees in the neighbourhood, it 
is curious that the nest should have been made, as it 
was, in a slight depression on the ground in the 
middle of a small plantation. Of the five eggs which 
the nest contained, but three hatched. Miss Turner 
gives some beautiful photographs of the female brood- 
ing her nestlings, which add greatly to the value of 
this unusual record. 
SoME new species of ectoparasitic trematodes are 
described in the June number of Zoologica, a publica- 
tion issued by the New York Zoological Society. 
NO. 2390, VOL. 95] 
All these stations, 
| NATURE 

[AUGUST 19, 1915 
Among these is a quite remarkable new genus repre- 
sented by two species. One of these, Atalostrophion 
sardae, infests the mucous membrane of the branchial 
cavity and the thyroid glands of the Bonito (Sarda 
sarda). So far no perfect specimen of an adult worm 
has yet been secured, nor does it seem likely that this 
will ever be done. And this because, in the sexually 
mature state, the body, which is about 6 in. long, and 
exceedingly fragile, is coiled in tangled masses among 
the tissues in which it lives, and since broken ends 
are always found when the specimens are examined 
in situ, it is to be assumed that it is natural for the 
worm to disseminate its eggs by throwing off the 
parted sections. Two complete specimens of imper- 
fect worms have, however, been secured, and these 
have been of the greatest service in determining the 
details of the anatomy of the adult, of which the 
largest fragments so far obtained have not exceeded 
3 in. in length. The other species was obtained from 
the gills of a large Jew-fish (Promicrops guttatus). 
This differed from that just described in being more 
muscular and less delicate. Sufficient materia], how- 
ever, has not yet been secured to enable a full 
diagnosis of its specific characters to be made. 
Tue March number of Terrestrial Magnetism and 
Atmospheric Electricity contains a report by Dr. W. F. G. 
Swann on the atmospheric electrical observations 
taken during the cruise of the Carnegie from Brook- 
lyn to Hammerfest, Spitsbergen, Iceland, Labrador, 
and home in the summer of 1914. The average value 
of the vertical potential gradient was 93 volts per 
metre, with a general increase in the value from 
summer to winter. The value agrees with the 80 volts 
per metre found by Simpson and Wright over the 
South Atlantic in 1910. The electrical conductivity of 
the air due to both positive and negative ions was 
2-52X10-* in electrostatic units, and increased to a 
maximum in September, in agreement with the re- 
sults found previously for the Atlantic. The average 
value of the earth-air current was 7-7X10~" electro- 
static units per sq. cm. The radio-activity was, on 
| the average, 23, in Elster and Geitel units, and corre- 
sponds to 12x 10-1? curies of radium emanation per 
cubic metre. Some of the decay curves suggest the 
presence of-thorium-B. None of the electrical elements 
observed showed any marked variations with tempera- 
ture or fraction of saturation of the atmosphere. 
In his paper on the equations of motion of a plane- 
kite (Bulletin of the Calcutta Mathematical Society, 
ii, I, pp. 25 et seq., now reprinted with additions), 
Prof. J. M. Bose has broken valuable ground 
on one of the many unsolved problems of aeronautical 
rigid dynamics. The assumptions on which the investi- 
gation is based lead to cubic equations for symmetric 
and lateral stability, instead of the biquadratics ob- 
tained for the aeroplane. This appears due to the 
author’s assumptions (1) that the kite is a plane 
surface without dihedral angles or keels, (2) that the 
line of action of the tension of the string meets the 
plane of the kite in a fixed point. Mr. C. V. Raman 
raises valid objections to the second assumption, which 
certainly does not hold good if the string is forked 
where it is attached to the kite, as shown in Prof. 

