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Wir# this issue appears the first of a series of 
supplements which it is proposed to publish from 
time to time dealing descriptively with subjects of 
_ wide scientific interest. The present supplement is 
devoted to a discourse delivered at the Royal Institu- 
tion on March 2 by Dr. G. C. Simpson, director of the 
Meteorological Office, and it provides in a convenient 
form a synopsis of existing knowledge of common 
meteorological phenomena. The method of dealing 
with the subject is characteristic of the present-day 
physicist, and it is essentially interesting. Satura- 
tion and relative humidities are somewhat fully 
described, and this is followed by a discussion of 
condensation at temperatures above the freezing 
point. It is of interest to note that the number of 
nuclei present in the air varies from a minimum of 
about 100 per c.c. to 100,000 or 150,000 per c.c. at 
imes in cities such as London and Paris. Condensa- 
tion nuclei are formed in various ways, one being the 
household fires and factory chimneys which produce 
large quantities of nucleus-forming material, chiefly 
sulphurous oxide. In England something like 5000 
tons of sulphur are burnt each day in coal fires, giving 
enough sulphur products to pollute the atmosphere 
of the whole of Great Britain. Haze and mist, 
though so much alike in appearance, appear to be 
foreign matter and a small amount of water, while 
mist is due to an actual precipitation of water from 
vapour to liquid. On the other hand, there appears 
to be no fundamental difference between mist and 
g, fog is generally only a dense mist. Above the 
g temperature inversion prevents all upward motion 
irly stationary and within a few hundred feet of the 
ground. Clouds, rain, thunderstorms, hail, snow, 
and other aspects of weather are so often topics of 
conversation that Dr. Simpson’s authoritative dis- 
course upon them will be welcomed by all scientific 
eaders. 
_ THE nomination of Sir David Bruce as president of 
the British Association for the meeting in Toronto 
next year is a well-deserved honour which will 
be gratifying to the many friends and admirers of 
this distinguished scientific investigator. Sir David 
_ belongs to the Royal Army Medical Corps, and early 
in his career made a name for himself by cultivat- 
ing the Micrococcus melitensis and establishing its 
_ Causative relationship to Malta fever by reproducing 
the disease in monkeys. Later, in 1904, he was the 
leader of the Royal Society’s Malta Fever Com- 
mission, which made the important discovery that 
fifty per cent. of the goats in Malta were infected and 
ten per cent. of them excreted the micrococcus in 
their milk. Within a year of prophylactic measures 
based on this fact being put in force, the cases at 
Malta fell to one-tenth of the former numbers, and 
since that time the Navy has been practically rid of 
one of the main causes of sickness in its personnel. Of 
still greater interest and importance are Sir David’s 
NO. 2789, VOL. 111] 
NATURE 
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597 

« Current Topics and Events. 
patient and well-thought-out researches on the 
greatest obstacle to the civilisation of tropical Africa, 
tsetse-fly disease of animals and man. His demon- 
stration of the Trypanosoma Brucei as the cause of the 
fatal tsetse-fly disease of cattle and horses in 1894 
paved the way for his demonstration in 1903 that 
“sleeping sickness is, in short, a human tsetse-fly 
disease,’’ by a wonderfully well conceived and worked- 
out experiment carried out as leader of a series of 
Royal Society Commissions working in Africa over a 
number of years. The etiology of two of the most 
important tropical fevers was thus elucidated by 
his investigations, with widespread results. Sir 
David is characterised by the thoroughness of his 
work and the intuition he has always brought to 
bear on every problem he has tackled. He is very 
fortunate in his helpmeet, Lady Bruce, who has 
shared in both the hardships and the scientific work 
of his many African expeditions. 
FIFTy years ago, on April 18, 1873, Justus von Liebig 
died at Munich at seventy years of age. In 1824, at 
the early age of twenty-one, he began his career 
as professor of chemistry at Giessen and he devoted 
the first twenty years of his academic work to 
researches in the field of organic chemistry and in 
developing and perfecting practical laboratory in- 
struction. The results of these labours quickly met 
with general recognition, and on his first visit to 
England Liebig was referred to by Faraday, at the 
meeting of the British Association at Liverpool in 
1837, as one of the greatest of living chemists. Great 
difficulties had to be overcome by Liebig when he 
began to extend his theoretical and practical work 
to biological problems. In 1840 he published 
“Organic Chemistry as applied to Agriculture and 
Physiology,”” and in 1842 “‘ Animal Chemistry, or 
Organic Chemistry as applied to Physiology and 
Pathology.’’ The doctrines of the nutrition of plants 
and animals contained in these epoch-making works 
were at first rejected by chemists, physiologists, and 
agriculturists, but most of them were established in 
the course of the following years. Liebig’s view that 
plants build up their organic parts exclusively from 
the carbon dioxide of the air and the water contained 
in the atmosphere and the soil, and that in intensive 
agriculture the mineral substances, especially potash, 
phosphoric acid salts, and nitrogen compounds, must 
be supplied to the soil in the form of artificial 
fertilisers, in addition to natural manure, was first 
accepted in England. After Liebig had modified his 
original opinion that the artificial fertilisers must be 
fairly insoluble in order not to be washed away by 
the rain, having recognised the extent to which the 
soil is capable of absorbing these substances, his 
doctrine of artificial fertilisation was generally 
accepted and forms the foundation of modern agri- 
culture. In 1864 and 1865 Liebig wrote, at the request 
of the Lord Mayor of London, important papers 
on the utilisation of the sewage of London. Other 
widely-known publications are those on meat extracts, 
