314 On the Energy expended in Propelling a Bicycle. 
This great efficiency of velocipedes when ridden slowly suggests that machines 
specially adapted to be ridden with the least possible effort at such low speeds as 
from four to six miles an hour, would be found useful for many purposes. A step 
in this direction has already been taken by the introduction of the excellent little 
“Facile” bicycle, with driving wheels sometimes as small as thirty-eight inches. And 
more would probably result from making machines of the tricycle class with driving 
wheels of from twenty-five tu thirty inches diameter, for going to one’s office in all 
weather, for shopping, for carrying parcels, for gently sauntering in the open air, 
for carrying invalids or children, and for many other useful purposes, to which 
velocipedes have as yet been little applied. 
The machine with which the experiments in this paper were made, was that 
known, as the “ Xtraordinary Challenge,” 1880 pattern, roller bearings to a front 
wheel of fifty-two inches, and cones to the hind wheel. The height of the rider is 
five feet eleven and a half inches ; length of leg, inside measure, thirty-six inches ; 
length of stroke, nine three quarter inches. The weight of the rider, ten and a 
half stones ; weight of machine sixty pounds. Hence the total weight of rider and 
machine was 207 pounds. ‘To adapt our results to a rider, whose weight along 
with that of his machine is more or less than this, all the energies recorded in Tables 
I. and II., would, of course, have to be altered in proportion to the change of 
weight. Thus, with a rider whose weight is thirteen and a half stones, the 
sauntering pace above spoken of was found to be nearer five than six miles. 
ADDENDUM. 
Since the foregoing pages were written we have constructed a chronograph, 
as suggested on page 308, and have been able to resume the investigation by the 
kinetic method. 
Our chronograph consists of a heavy pendulum to the rod of which a pencil is 
attached a few inches from the fulcrum. Behind the pendulum a vertical board 
is placed, mounted so that an assistant can by a winch make it travel upwards 
while the pendulum is swinging. To this board strips of paper, about five feet in 
length are fastened by drawing pins, and on this paper the pencil attached to the 
pendulum traces a wavy line in the form of a rough curve of sines. It only 
remained to have another pencil mounted on a trigger to produce dots at the 
will of the observer, and the position of these dots in relation to the curve of 
sines, gives with sufficient precision the times at which the dots are produced. Tho 
observations were made as follows :—One of us rode the bicycle, getting up a 
speed of from fourteen to sixteen miles an hour, then took his feet off the treadles 
and ran the machine without propelling it, till the speed fell to about four miles 
an hour. Meanwhile the other manipulated the trigger of the chronograph, and 
thus recorded the instants at which one treadle in successive revolutions reached its 
