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[iv] be, the importance and singularity of the subjects, or the advantageous manner of treating them, without pretending to answer for the certainty of the facts, or propriety of the reasonings, contained in the several papers so published, which must still rest on the credit or judgment of their respective authors.

It is likewise necessary on this occasion to remark, that it is an established rule of the Society, to which they will always adhere, never to give their opinion, as a Body, upon any subject, either of Nature or Art, that comes before them. And therefore the thanks which are frequently proposed from the Chair, to be given to the authors of such papers as are read at their accustomed meetings, or to the persons through whose hands they receive them, are to be considered in no other light than as a inatter of civility, in return for the respect shewn to the Society hy those communications. The like also is to be said with regard to the several projects, inventions, and curiosities of various kinds, which are often exhibited to the Society; the authors whereof, or those who exhibit them, frequently take the liberty to report, and even to certify in the public newspapers, that they have met with the highest applause and approbation. And therefore it is hoped, that no regard will hereafter be paid to such reports and public notices; which in some instances have been too lightly credited, to the dishonour of the Society.

THE PRESIDENT and Council of the Royal Society adjudged the Medal on Sir Godfrey COPLEY's Donation, for the year 1809, to Mr. EDWARD TROUCHTON, for the Account of his Method of Dividing Astronomical Instruments, printed in the last Volume of • the Philosophical Transactions.



I. The Croonian Lecture. By William Hyde Wollaston, M. D.

Sec. R. S.

Read November 16, 180g.

I am aware that the remarks, which I have to offer on the present occasion, may be thought to bear too little direct relation to each other for insertion in the same lecture; yet any observation respecting the mode of action of voluntary muscles, and every enquiry into the causes which derange, and into the means of assisting the action of the heart and bloodvessels, must be allowed to promote the design of Dr. Croone, who instituted these annual disquisitions. And it has always appeared to be one great advantage attending the labours of this Society, that it favours the production of any original knowledge, however small, in a detached form ; and enables a writer to say all that he knows upon a particular subject, without inducing him to aim at the importance of a long dissertation.



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I shall therefore make no apology for dividing the following 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 deranging 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.

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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 physiologists; 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, unless 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 extremity of the finger into the ear. A sound is then perceived which resembles most nearly that of carriages at a great distance passing rapidly over a pavement.

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