STEAM-SHIPS FOR THE CHANNEL PASSAGE. 
3 
is the leading one. We know that there is mechanical cause. 
When a man is standing or sitting, the weight of his intes- 
tines is taken by the pelvic bones, and through the reaction of 
these there is but little upward pressure against the stomach, 
diaphragm, and liver, which are supported by the scaffolding 
of the spine and ribs. When this reaction is prevented by the 
ship sinking from under one’s feet, the elasticity of the intes- 
tines is no longer controlled by gravity, and they are free to 
press upwards against the stomach and other organs. Else- 
where than at sea, we know that this relief of weight does pro- 
duce uneasiness. A qualm is felt in the descent from a swing, 
and in jumping feet foremost from great heights, while no 
such feeling is experienced in a high dive taken head foremost. 
The alternation of this pressure is quite a sufficient cause of 
irritation to produce sickness. A very remarkable confirmation 
of this view is afforded by the fact that sea-sickness in women 
occasionally presents different and far more serious symptoms 
than it is usual to meet with in the case of men. 
Whether the optical effect be alone sufficient to produce sea- 
sickness in an ordinary person may be open to doubt ; but 
there is no denying that it very much enhances whatever effects 
may be due to the mechanical causes, especially the distressing 
giddiness which is a frequent symptom. Giddiness is not 
solely due to optical causes. I have seen a child make itself 
sick by turning round and round with its eyes shut. I draw 
from this the further inference that the amount of motion 
necessary is not very great, if it be sufficiently long continued. 
The upward and downward motion on board a ship is due 
not only to the upward and downward movements of the ship 
as a whole, but also to the rocking, whether rolling or pitching ; 
just as in a see-saw the ends of the plank move up and 
down, although the plank, as a whole, has no vertical motion, 
seeing that it turns on a fixed pivot. There is no such fixed 
pivot in a ship : every point of it moves ; but at the extreme 
ends and sides this see-sawing is added to the unsteadiness of 
the middle part of the ship, which accordingly seems to be 
comparatively still. 
The uneasiness of a ship is greatly enhanced by the con- 
tinually varying mixture of heaving, rolling, and pitching, 
which prevents our adapting ourselves to the motion in the 
same way that a little muscular action, combined with the 
selection of a suitable attitude, enables us to meet a simple 
oscillation like that of a swing. Any mechanism which sim- 
plifies the motion will therefore probably tend to reduce sea- 
sickness. 
One point, which is common to all the improved designs of 
ships for the channel passage^ is large size. The harbours on 
