378 
VELOCITY AND PRESSURE INSTRUMENTS. 
each of these minute spaces, and, from the velocities, the mean pressures 
necessary to produce them are obtained. These calculations are extremely 
laborious. The rounds are worked out by Captain Noble (the inventor of 
the instrument) and an assistant, using two calculating machines, to check 
one another, and many hours of hard work are required in calculating the 
pressures for each round. The method of arriving at the velocities, as 
shown in the foregoing tables, is a comparatively simple matter. 
Woolwich, 
10th January, 1876. 
