470 
NATURE 
[APRIL 7, 1923 

without intermission—Sundays, Bank Holidays, and 
Christmas Day—for a whole year. A mass of data 
was obtained of high statistical value which is proving 
of the greatest importance in the study of the soil 
population. One of the most interesting results was 
the proof that the soil population is not steady in 
number as had always been assumed, but is in a violent 
state of flux. Every organism observed—protozoon 
or bacterium—showed great daily variations, which 
seemed to be independent of external conditions. At 
least one showed a two-day periodicity. The fluctua- 
tions of the amcebe were of special interest as they were 
exactly the reverse of the bacterial fluctuations. Close 
examination of the curves leaves no doubt that the 
fluctuations of the amcebe cause the fluctuations of 
the bacteria, high numbers of amcebe causing low 
numbers of bacteria, and low numbers of amcebe 
allowing bacterial numbers to rise: but why the 
amcebee fluctuate remains a mystery. 
In the case of bacteria it has been possible to make 
even closer observations. A census organised by 
Messrs. Thornton and Page has been taken each two 
hours for several days and nights ; but again the same 
wonderful fluctuations are seen. As might be ex- 
pected, the amount of work, as measured by the nitrate 
present, alters from hour to hour. But the curve was 
not quite what was expected : the increases in amount 
of nitrate could be understood as representing the 
work done by bacteria, but the decreases were more 
difficult to explain. There was no rain to wash it 
out and there were no plants to take it up; yet the 
nitrate tends to disappear. The results suggest that 
some organism is absorbing it. Algee and fungi could 
both do this, and both are found in the soil : Dr. Muriel 
Bristol and Dr. Brierley are closely studying them. 
Perhaps even more remarkable than the daily 
changes are the great seasonal changes. It appears 

The Present and Future 
ia shipping and shipbuilding are passing 
through a period of severe depression it is 
generally considered that more prosperous times are 
in sight. The War, as is well known, occasioned 
tremendous losses to the shipping of the world—we 
ourselves lost over seven million tons—but this has 
been more than made up, and the latest edition of 
Lloyd’s Register Book shows that there are afloat 
to-day, exclusive of sailing vessels and vessels under 
roo tons, some 29,000 steam and motor ships of a total 
tonnage of 61,000,000 tons. This is an increase of 
some 14,000,000 tons on the figures for 1914, but 
while in that year the United Kingdom owned nearly 
443 per cent of the world’s sea-going steam tonnage 
our present proportion is just over 334 per cent. In 
spite of this, we are still the greatest users of ships 
and the greatest builders of ships, though to-day 
shipping returns are only too eloquent of ships laid up, 
berths empty, shops closed, and machinery idle. 
While this is the case, the competition for such 
orders as are to be obtained has forced all designers 
to study more closely than ever the economics of 
shipbuilding and marine engineering, and a vast 
amount of investigation and research is being carried 

that the whole soil population is depressed in winter 
and in summer, and is uplifted in spring and autumn. 
How this comes about we do not know. The pheno- 
menon does not seem to be confined to the soil; the 
alge in a pond and the plankton in the sea, like the 
organisms in the soil, all seem to feel the joy of spring ; 
it is as if Virgil had got hold of some great truth in 
natural science, which we have not yet been able to 
express in cold scientific terms, when he says that in 
spring “ Aether, the Almighty Father of Nature, 
descends upon the earth, and blending his mighty frame 
with hers, gives life to all the embryos within.” 
(‘‘ Georgics,” Bk. II. 11, 324-327). 
The number of organisms in one single gram of soil— 
no more than a teaspoonful—often well exceeds 4o 
millions. This looks big, but it is difficult to form an 
idea of its immensity. If each unit in the whole array 
could be magnified up to the size of a man and the whole 
caused to march past in single file, they would go in a 
steady stream, every hour of the day and night for a 
year, a month and a day, before they had all passed. 
We must think then of the apparently lifeless soil which 
we tread beneath our feet as really throbbing with life, 
changing daily and hourly in obedience to some great 
laws which we have not yet discovered ; pulsating with 
birth, death, decay, and new birth. And if the wonder 
were not sufficient, we know that in some way these 
lowly organisms are preparing the food for our crops— 
the crops on which we ourselves feed. It is possible— 
it is even probable—that our attempts to learn some- 
thing of this wonderful population may lead to some 
degree of control which would have valuable economic 
results. But even if this never happened the work 
would still be justified because it shows to the country- 
man something of the abounding interest of his daily 
task and of the infinite wonder of the soil on which he 
spends his life. 
of Marine Engineering. 
out. Especially noteworthy are the inquiries being 
made into the respective advantages of the steam 
engine, the steam turbine, and the oil engine. As a 
result of this, the shipowner is to-day offered a be- 
wildering variety of machinery of various types, all 
of which have their respective merits. A quarter of 
a century ago marine machinery was more or less 
standardised. Practically every ship built then was 
fitted with cylindrical boilers burning coal, and triple 
expansion engines. Of the 61,000,000 tons of shipping 
referred to above, 51,000,000 tons are still driven by 
such engines. Remarkably successful as it has been, 
the reciprocating steam engine, however, has long been 
superseded in naval vessels and fast liners by the 
steam turbine, and now its very existence is threatened, 
on one hand by the turbine combined with mechani- 
cal, hydraulic, or electric transmission gear, and on the 
other hand by numerous forms of the Diesel internal 
combustion engine. , 
The present position of the marine steam turbine is 
scarcely less critical than that of the triple expansion 
engine. It is twenty-one years since the marine 
steam turbine was used commercially, and it is esti- 
mated that turbines of more than 50,000,000 horse- 

