Page:Philosophical Transactions - Volume 050, part 1.djvu/53

 after dressing); so that the water was not quite still when they got into the cistern: neither could I persuade all of them to lay themselves down gently, much less to keep their heads under water so long a time as one second: so that, in most of the observations, the surface of the water was far from being quite so still, as to render the measures perfectly exact, I being obliged to catch them, as it were, by taking the mean height between the librations. Moreover, the great area of the cistern was no inconsiderable bar to the accuracy I expected. However, as I do not recollect experiments of this kind anywhere recorded, these, perhaps, may give some satisfaction to such persons, who may have the curiosity to desire some knowlege on this subject. Were I to make any more observations of this kind, I would chuse an upright parallelopiped, not above 18 or 20 inches in the side of the square; into which the person should let himself down by steps nailed to the side: for in so small an area the motion of the water would sooner subside; neither would the librations be any thing near so large as on a smaller surface.

One of the reasons, that induced me to make these experiments, was a desire of knowing what quantity of fir or oak timber would be sufficient to keep a man afloat in river or sea water, thinking that most men were specifically heavier than river or common fresh water; but the contrary appears from these trials: for, excepting the first and last, every man was lighter than his equal bulk of fresh water, and much more so than his equal bulk of sea-water: consequently, could persons, who fall into water, have presence of mind enough to avoid the fright. 50.