THE ROYAL ARTILLERY INSTITUTION. 
161 
DESCRIPTION 
OF A 
CHRONOGRAPH 
ADAPTED FOR MEASURING THE VARYING VELOCITY OF A BODY IN 
MOTION THROUGH THE AIR, AND FOR OTHER PURPOSES. 
by # 
FRANCIS BAS1IFORTH, B.D., 
PROFESSOR OF APPLIED MATHEMATICS TO THE ADVANCED CLASS OF 
ARTILLERY OFFICERS, WOOLWICH, 
AND LATE FELLOW OF ST JOHN’S COLLEGE, CAMBRIDGE. 
[COMMUNICATED BY THE SECRETARY R.A. INSTITUTION.] 
The resistance of fluids to the motion of solids is a problem of great 
practical and theoretical interest, because sometimes this resistance becomes 
a source of power, whilst at other times it is a large consumer of power 
which would otherwise be usefully applied. Thus the action of the wind 
upon sails is made to drive a mill or a ship. The wind acting upon the sails 
tends to drive the ship, and the resistance of the water is opposed to the 
progress of the ship. The resistance of the water to the motion of the oar, 
the paddle, or the screw, enables the rowers or the steam engine to drive 
the vessel. A very large part of the power developed in the locomotive is 
employed in overcoming the resistance of the air to the motion of the train. 
And quite recently it has been found that the friction of the tidal wave is 
probably slowly diminishing the velocity of the earth's rotation about its 
axis. We are dependent upon the resistance of fluids for our power to 
cross the ocean, for without that property we should not be able to use sail 
or oar, paddle or screw. Still little is known with accuracy respecting the 
laws of the resistance of fluids. It is extremely difficult to make satisfactory 
experiments on account of the great disturbance produced in the surround¬ 
ing fluid, and as the mathematician knows neither the nature of this 
disturbance, nor the amount of resistance to be accounted for in particular 
cases, he is not able to find ground on which to base a satisfactory theory. 
Eor a history of what has been done, it will suffice to refer to the articles, 
“Ballistik" and "Widerstand," in Gehler’s Physikalisch.es Worterbuch, 
1825 and 1842. 
The resistance of the air to spherical balls, moving with high velocities, 
has been a subject of special interest for more than a century, because it 
was of practical importance to the science of gunnery, and because it offered 
