2 
Dr. Wollaston on the Duration 
I shall therefore make no apology for dividing the follow- 
ing lecture into three distinct parts. 
In the first of which I shall treat of the duration of volun- 
tary action. 
In the second, I shall attempt to investigate the origin of 
sea-sickness, as arising from a simple mechanical cause de- 
ranging the circulation of the blood 
In the third, I shall endeavour to explain the advantage 
derived from riding and other modes of gestation, in assisting 
the health under various circumstances, in preference to every 
species of actual exertion. 
Part I. On the Duration of Muscular Action. 
The necessity of occasional intermissions from a series of 
laborious exertions, is within the experience of every one ; the 
fatigue of continuing the effort of any one voluntary muscle 
without intermission even for a few minutes is also sufficiently 
known ; but there is a third view of the duration of muscular 
action which appears to have escaped the notice of physiolo- 
gists ; for I believe it has not hitherto been observed that each 
effort, apparently single, consists in reality of a great number 
of contractions repeated at extremely short intervals : so short 
indeed that the intermediate relaxation cannot be visible, un- 
less prolonged beyond the usual limits by a state of partial or 
general debility. 
I have been led to infer the existence of these alternate 
motions from a sensation perceptible upon inserting the extre- 
mity of the finger into the ear. A sound is then perceived 
which resembles most nearly that of carriages at a great dis- 
tance passing rapidly over a pavement. 
