ig Dr. Wollaston on Sea-Sickness. 
who has not been so situated, can form a just conception 
of it.* 
In thus referring the sensations of sea-sickness in so great 
a degree, to the agency of mere mechanical pressure, I feel 
confirmed by considering the consequence of an opposite mo- 
tion, which by too quickly withdrawing blood from the head, 
occasions a tendency to faint, or that approach to fainting, 
which amounts to a momentary giddiness with diminution of 
muscular power. At a time when I was much fatigued by 
exercise, I had occasion to run to some distance, and seat my- 
self under a low wall for shelter from a very heavy shower. 
In rising suddenly from this position I was attacked with 
such a degree of giddiness, that I involuntarily dropped into 
my former posture, and was instantaneously relieved by re- 
turn of blood to the head, from every sensation of uneasiness. 
Since that time, the same affection has frequently occurred 
to me in slighter degrees, and I have observed, that it has 
always been under similar circumstances of rising suddenly 
* There is one occasion upon which a slighter sensation of this kind is perceived, 
and it appears to indicate the direction of the motion from which it arises, to be 
downwards. <c In a country subject to frequent returns of earthquakes ” it is said * 
that tf a few minutes before any shock came, many people could foretel it by an al- 
teration in their stomachs ; an effect which ” (it is added) “ always accompanies the 
wave-like motion of earthquakes, when it is so weak as to be uncertainly distinguish- 
able.” (Michell, Phil. Trans. Vol. LI. 610.) 
It seems that the vapours to which these tremendous concussions are owing, im- 
mense in quantity, and of prodigious force, being for a time confined on all sides, 
elevate the surface of a country to a vast extent until they either find vent, or meet 
with some partial cause of condensation, and hence the alternate heaving and subsi- 
dence of the ground, will produce much the same effects as the rising and falling of 
the swell at sea. 
* Phil. Trans. Vol. XL 1 I. p. 41. 
/ 
