1879J Measurement of Powder Pressures in Cannon. 359 
account of the decomposition which the manure must first 
undergo before it can exercise its a( 5 tion. 
M. Ville strongly advocates the foundation of experimental 
fields. They are, he affirms, the only reliable method of 
ascertaining with certainty the composition of the soil with 
respeCt to the requirements of agriculture. A piece of land 
should if possible be selected which in its physical nature 
and degree of fertility represents the average quality of the 
land that is to be cultivated. For a newly-worked farm the 
field should consist of twenty plots, each containing about 
four poles, arranged in two parallel rows of ten plots each. 
The first row should be devoted to the cultivation of wheat, 
and the second to that of beet-root or potatoes, according to 
the dimate and the wants of the district. The wheat fur- 
nishes indications of the richness of the superficial layers of 
the soil, and the beet-root of the deeper layers. Full instruc- 
tions are given respecting the manuring of the several plots. 
M. Ville also gives directions for establishing experimental 
fields for agricultural colleges, societies, and for elemen- 
tary schools. For the latter the plots should be about 
eleven yards square. By carrying out the advocated system 
of manuring it will be conclusively established that it is 
possible to farm without using farmyard manure ; that a 
manure can be and is composed which more than takes its 
place, and that the aCtion of animal manure is intensified by 
the addition of chemical manure. 
VIII. MEASUREMENT OF POWDER PRESSURES 
IN CANNON BY MEANS OF THE REGISTERED 
COMPRESSION OF OIL. 
S HE determination of the pressure exerted by the elastic 
gases produced by the combustion of gunpowder is an 
element of the first importance in the theory and 
practice of gunnery, and a measure of this pressure is indis- 
pensable in all mathematical computations of the effects of 
gunpowder on the projectile or on the gun. 
