338 
MR. FARADAY ON THE FORMS AND STATES 
enough water on it, either from the receding tide or from the shingles above, 
to cover it thoroughly, but not to form waves, be observed in a place where 
the wind is not broken by pits or stones, stationary undulations will be seen 
over the whole of the wet surface, forming ridges like those already described, 
and each several inches long. These are not waves of the ordinary kind ; they 
are accurately parallel to the course of the wind ; they are of uniform width 
whatever the extent of surface, varying in width only as the force of the wind 
and the depth of the stratum of water varies. They may be seen at the windward 
side of the pools on the sand, but break up so soon as waves appear. If the 
waves be quelled by putting some oil on the water to windward, these ripples 
then appear on those parts. They are often seen, but so confused that their 
nature could not be gathered from such observations, on the pavements, roads, 
and roofs when sudden gusts of wind occur with rain. The character of these 
ripples, and their identity with stationary undulations, may be ascertained by 
exerting the eye and the mind to resolve them into two series of ordinary 
advancing waves moving directly across the course of the wind in opposite 
directions. But as such series could not be caused by the wind exerted in a 
manner similar to that by which ordinary waves are produced, (the direction 
being entirely opposed to such an idea,) I think the effect is due to the water 
acquiring an oscillatory condition similar to those described, probably in- 
fluenced in some way by the elastic nature of the air itself (124) and ana- 
logous to the vibration of the strings of the /Eolian harp, or even to the vibra- 
tion of the columns of air in the organ-pipe and other instruments with em- 
bouchures. 
These ridges were strong enough to arrange the sand beneath where ordi- 
nary waves had not been powerful enough to give form to the surface. 
123. All the phenomena as yet described are such as take place at the sur- 
faces of those fluids in common language considered as inelastic, and in which 
the elasticity they possess performs no necessary part; nor is it possible that 
they could be produced within their mass. But on extending the reasoning, it 
does not seem at all improbable that analogous effects should take place in 
gases and vapour, their elasticity supplying that condition necessary for vibra- 
tion which in liquids is found in an abrupt termination of the mass by an un- 
confined surface. 
