DON? 

in which an account of the islands is given, and their 
importance for the production of copra is described. 
The soil is very fertile, volcanic in origin, mixed with 
coral limestone, and with the rainfall averaging 
90-200 ins., and a very humid climate, the coconut 
palm flourishes and bears very heavy crops. Some 
25,000 acres are now under coconut plantations in the 
various islands. The palms come into bearing very 
early, and the writer of the letter records that he saw 
a tree under six years old bearing considerably more 
than 300 nuts, which is by no means a record for 
these islands. As the Solomon group lies on the 
direct route between Australia and the Philippines and 
Japan, the importance of the islands is likely to 
increase in the near future. 
In the current number (vol. xiii, No. 1) of 
the Bulletin of the Imperial Institute attention 
is directed to the economic resources of the 
German colonies, and in particular to the agricultural 
and forest products of German East Africa. Copra, 
ground nuts, sesame seeds, oil palms, beeswax, cotton, 
coffee, grain, sugar-cane, and tobacco, all of which 
are in native hands, are among the products especially 
considered. The German East Africa Company also 
conducts a considerable sisal hemp industry—more 
than 367,000l. worth being exported in 1912—and there 
is extensive European cultivation of cotton, kapok, 
plantation rubber, and gutta-percha. The exports of 
the two latter products in 1912 reached the combined 
value of more than 362,o00l. The bulk of the products 
went to Germany, but some of the rubber, coffee, copal, 
hides, and ivory have been coming to the United 
Kingdom. 
Tue Kew Bulletin No. 3 contains papers dealing 
especially with questions of systematic botany, in- 
cluding descriptions of several new species. In notes 
en South African Santalaceze Mr. Hill describes three 
new species of the singular little dicecious genus 
Thesidium. In some of the species the male and 
female plants are so dissimilar that unless found grow- 
ing together, their relationship would not be recog- 
nised. A remarkable etymological invention originating 
with a misprint is pointed out in connection with the 
generic name Frisca, a synonym of Thesium, a mis- 
print for Th. Frisea, a Linnean species of Thesium. 
Wettstein, in his ‘‘ Etymologisch-botanisches Hand- 
worterbuch,”” has ‘‘Frisca (Santalaceze). Nach Th. 
Frisca, der sich am Cap im botanischen Interesse 
aufhielt.’? The mistake in spelling is due to End- 
licher and Spach, but Wettstein is responsible for 
evolving from what is merely the name of.a plant 
a person who in the interests of botany sojourned at 
the Cape. 
Dr. C. F. Jurirz, Government analyst, Cape Town, 
has recently visited the prickly pear station at 
Dulaceca, Queensland, and contributed an interesting 
account of the prickly pear problem in Australia, which 
has been reprinted from the Cape Times and Farmer's 
Record for February 5. His account deals with the 
methods undertaken under the supervision of Dr. 
Jean White to eradicate the Opuntia and clear areas 
for cultivation. Of the two methods employed, the 
NO. 2378, VOL. 95] 
NATURE 
[May 27, 1915 



effects of chemicals and the introduction of cochineal, 
the former is likely to be more effective, since the 
insect has no effect on the most prevalent species, 
O. inermis and O. aurantiaca, which are protected by 
a layer of subcutaneous cells containing calcium 
oxalate. Of chemicals only those containing arsenic 
are of any practical value, and the effect of the gas 
arsenic trichloride appears to be very promising. The 
cost of destruction works out at about 15s. per acre. 
The use of the Opuntia as a source of potash and as a 
source of industrial alcohol promises some return on 
the outlay for destruction. 
Tue Cairo Scientific Journal for September, 1914, 
contains an extremely interesting and valuable discus- 
sion of ‘‘The Frequency of Cloud-forms at Helwan, 
1904-1913,” by Mr. N. A. Comissopulos. Helwan is 
situated about eighty miles west of Suez and about 
130 miles south-east of Alexandria. The discussion 
is suggestive in its method and arrangement, and 
well deserves to be imitated by other observers. The 
times of observation are § and 11 a.m., and 2, 5, and 
8 p.m. each day, and the clouds have been tabulated 
and classified to determine their annual and diurnal 
variations. Cirrus clouds are shown to be the most 
frequent of all clouds; they attain their absolute maxi- 
mum in May and their absolute minimum in July, 
whilst the cirro-stratus attains two maxima during the 
year, in December—January and in April, and the 
absolute minimum is attained in September. Other 
upper clouds are somewhat irregular. Intermediate 
clouds, as alto-cumulus and alto-stratus, were rarely 
seen. For lower clouds it is mentioned that the pro- 
gress of nimbus is regular, the maximum occurs in 
January and the minimum in July; stratus has two 
distinct maxima, one in April and the other in October, 
with an absolute minimum in June and July. Fogs 
occur principally in the early morning and during the 
winter months. Forty-nine per cent. of all observa- 
tions are clear skies, which shows the relative dry 
character of the Egyptian weather. The grouping of 
the clouds for the diurnal variation also gives fairly 
regular results. 
THE papers contributed to a general consideration 
of the hardening of metals, together with the dis- 
cussion to. which they gave rise at a recent meeting 
of the Faraday Society, of which an account was given 
in Nature of December 3, 1914 (vol. xciv., p. 374), 
have been reprinted as a brochure by the society with 
certain additions. The latter include communications 
from Arnold, Rosenhain, and Thompson. The 
pamphlet thus gives in a compact form an up-to-date 
summary of the principal current theories of harden- 
ing. After reading it, it is impossible not to be struck 
by the far-reaching influence of Beilby’s theory of the 
vitreous-amorphous and crystalline conditions of metals 
and alloys in its bearing on this question, in spite of 
the statement of Arnold that ‘‘no modern theories have 
disturbed to any great extent the explanation of the 
hardening of steel made by Henry Clifton Sorby a 
lifetime ago.” . 
Tue June and July, 1914, numbers of the Journal 
de Physique, which is now conducted by the French 





