798 
desired to introduce. 
** gins ”’ and presses is also likely to be introduced. 
All these measures are an example of energetic and 
purposeful action taken by Government, under the 
inspiration of results achieved by research in the 
interests of agriculture. The progress already made 
has, no doubt, been favoured by the great field which 
the Indian crops provide for plant improvement. 
(There is no space to tell of the achievements in the 
breeding of sugar-cane, but the distressed agriculturists 
of Great Britain will read with envy of a crop of an 
improved variety of sugar-cane yielding 60 tons of raw 
cane per acre, as against a normal 20 tons, worth at a 
moderate estimate 60/.) But when favourable condi- 
tions are allowed for, there remains the fact that the 
Government appreciates, and has been quick to develop 
economically, the results of scientific work. It was not 
content to let these results rest at the laboratory stage. 
What could be accomplished by similar methods in 
Great Britain it is difficult to say ; some remnants of en- 
lightened despotism still linger in India, and can be used 
quickly and effectively in the interests of progress ; but 
it might be worth considering whether in the present 
sorry plight of agriculture some measure of action 
similar to that followed in India could not be taken. In 
particular, the idea of creating a research fund by the 
levy of a cess on the product that it is desired to 
improve may be worthy of consideration. Bacon, 
cheese, butter, wool, flax are examples of products that 
are imported into Britain in large quantities, to the 
detriment of the home producer. Is organised research 
powerless to help? There can be no doubt as to the 
answer, but our politicians, while ready to give lip- 
service to the value of “ education and research,” and 
even grants of money in aid of experimental work, have 
failed to show an adequate appreciation of the need of 
following up the achievements of research by adminis- 
trative action, such as that so effectively taken by the 
Government of India. 

Shield Tunnelling. 
Shield and Compressed Air Tunnelling. By B. H. M. 
Hewett and S. Johannesson. Pp. x+465. (New 
York and London: McGraw-Hill Book Co. Inc., 
1922.) 255. 
( F late years engineers have been driven more and 
more to find a location for railways, roadways, 
and large water-mains below the surface of the ground. 
In cities, by going underground the cost of acquiring 
valuable property is escaped. In crossing rivers, a 
tunnel may be less expensive than a bridge. A method 
has been devised for tunnelling in soft or water-bearing 
ground in which the miners work in a shield and an 
NO. 2798, VOL. 111 | 
NATURE 
The official regulation of cotton | inrush of water 1s prevented by compressed air. In 

[June 16, 1923 
this method rings of cast-iron segments are erected in 
the shield, forming a water-tight lining, and as each 
section is completed the shield is driven forward by 
hydraulic jacks, leaving the lining to support the rock 
or earth. The more difficult the ground the greater is 
the advantage of this method of working. The number 
of tunnels which have been so driven in different 
countries is now large, but though the method is simple 
in principle the difficulties and dangers met with in 
carrying it out are among the most serious which tax 
the skill and experience of the engineer and contractor. 
Information about shield tunnelling is scattered in 
the proceedings of professional societies, and the treatise 
of Messrs. Hewett and Johannesson is one of the first 
in which the data of past experience are gathered 
together and the attempt is made to formulate 
principles and rules of practice. It is an excellent 
treatise, full of information, well illustrated, and com- 
petently discussed. 
Brunel patented the first shield, and by its help over- 
came the very great difficulties of driving the first 
tunnel under the Thames (1825-1843). In 1869, 
Barlow promoted the construction of the Tower Subway 
for foot passengers under the Thames. When con- 
tractors feared to undertake the work, a young engineer, 
Greathead, designed a new form of shield and completed 
the tunnel in a year. This was in dry London clay. 
Then, when such difficulty was experienced in driving 
the two Hudson River tunnels in water-bearing silt at 
New York that the work was temporarily abandoned, 
Greathead and Baker carried it on for 2000 feet by a 
shield and compressed air. Stopped again by want of 
capital, the tunnels were completed in 1904 by Jacobs. 
Later the Blackwall and Rotherhithe tunnels under the 
Thames and others abroad were successfully con- 
structed by the same method. Descriptions of these 
and a full bibliography are given in this treatise. 
The cast-iron lining for shield-driven tunnels is now 
in general use. The space between the lining and 
ground is filled by cement grout, forced by compressed 
air through holes in the lining, and the interior is made 
fair by brick or concrete. The joints of the lining are 
caulked with rust cement. There is a bulkhead behind 
the shield through which the compressed air is forced, 
and it contains airlocks for men and materials. The 
shield is driven forward by hydraulic jacks, working 
with pressures up to 6000 pounds per sq. in. and 
exerting a total force amounting to 6000 tons in some 
cases. Usually in the shield is a hydraulic erector for 
lifting and placing the cast-iron segments and mechani- 
cal excavators for removing the soil at the face. It 
may give an idea of the complex arrangements neces- 
sary if it is stated that among the equipment required 
