XXII.—ON THE ENERGY EXPENDED IN PROPELLING A BICYCLE. 
By G. JOHNSTONE STONEY, D.SC., F.R.S., A VICE-PRESIDENT OF THE SOCIETY ; AND G, 
GERALD Stoney.— With Puates XXXIX., XL., anp X LI. 
[Received August, 1882.] 
The magnitude of the effects produced by human muscles acting upon bicycles 
and tricycles is well deserving of attention. Several riders of exceptional strength 
and endurance have travelled considerably more than 200 miles in one day, along 
common roads; another has twice maintained an average speed of more than 
twenty miles an hour along a prepared path for a whole hour ; another has ridden 
from the Land’s End to John O’Groat’s, a distance of almost 1,000 miles, in thirteen 
days, averaging more than seventy-six miles a day. These astonishing feats have 
been accomplished upon bicycles, and the tricycle does not fall far behind. <A 
tricycle has been ridden a distance of 180 miles in one day; and hundred mile 
journeys on both classes of machines have become frequent. It is perhaps quite 
as striking that average riders, who are not athletes, even including those who are 
between fifty and sixty years of age, usually in touring make from thirty to sixty 
miles a day without pressing themselves, going on day after day without inter- 
mission and without fatigue. 
Such an astonishing efficiency ought to be capable of explanation ; and as it is 
plain that no sound knowledge on the subject can be gained without first ascer- 
taining experimentally the amount of energy actually expended in propelling a 
bicycle, we have endeavoured to make this determination. 
The machine known as the “ Xtraordinary” offers facilities for attaching an 
indicator diagram apparatus to it, and was that upon which the experiments were 
made. It is represented in Figure 1, Plate 39. Indicator diagrams were obtained 
in two different ways, which furnished independent series of observations, adapted 
to test each other. Further to confirm our results, we endeavoured to measure the 
energy by a kinetic method, by taking the feet off the treadles when the machine was 
running at high speed, and leaving it to advance by its own impetus (?.e., kinetic 
energy) until the rate was too slow for the rider to maintain a steady balance, 
After some practice the skill required to carry out this programme was attained, 
and the observations were made by an assistant noting the times occupied in per- 
forming successive sets of five revolutions of the wheel. Starting with a speed of 
about fourteen miles an hour, four, and in some cases five, such sets could be 
observed before the motion became unsteady. From these data the energy re- 
quired to drive a bicycle at the speeds successively passed through could be 
deduced. The results which we were able to obtain by this method, so far as they 
go, seem to confirm the more reliable deductions from the indicator diagrams, but 
TRANS. ROY. DUB. SOC., N.S., VO I. 3K 
