156 MR. J. P. JOULE ON THE UTILIZATION OF THE 
population. Yet there are many who treat the subject 
entirely as a commercial one, and if the cost of transit is 
such as to prevent sewage competing with guano in the 
market, they argue that it ought to be thrown away as 
refuse. But this is a fallacious, narrow-minded and selfish 
view of the subject. In order apparently to save ourselves 
a little money at the present moment it entails a heavy 
burden-on the inhabitants of the country in subsequent 
years. Guano will not last for ever. According to the 
Peruvian Survey the Chincha Islands can yield 18,200,000 
tons. Of this quantity Great Britain alone consumed in 
1857 no less than 288,362 tons, which, if we consider the 
entire waste of sewage in Great Britain to be double that 
of London, will almost exactly make up for it in money 
value. If the produce of the above islands, which afford 
the best guano, be reserved for the sole use of Great Bri- 
tain, it will last only sixty-three years at the present rate 
of consumption. JI am aware that other supplies have 
been found in various parts of the world, and that there is 
a trifling additional deposit each year. But when we con- 
sider the competition which will eventually take place on 
the part of other countries to secure so valuable a manure, 
and also the ever increasing difficulties of obtaining it, we 
cannot trust to our being able to import it in the quanti- 
ties we now do for even so long a period as that above 
named. 
In addition to the help derived from guano, the soil of 
Britain is relieved from the present effects of sewage waste 
by large importations of corn and cattle and of bone ma- 
nure. But such a supply can continue only so long as 
foreign governments remain in ignorance of the permanent 
injury sustained by their fields. Liebig, in his Agricul- 
tural Chemistry, complains that, if the exportation of bones 
continued on the then scale, the German soil would be- 
come gradually exhausted. 
