730 Marvels of the Universe 
Photoby) (EZ. Step, F.LS. 
RANATRA. 
A group of these remarkable Water Bugs in natural attitudes and life size. The curious resemblance to the unrelated 
Stick Insects is strikingly shown. Note the Mantis-like development of the first pair of legs. 
dive into the depths. It is noteworthy that neither Ranatra, Water Scorpion, nor Boatman is 
provided with antenne. 
SAND-WAVES AND SAND-RIPPLES 
BY EDWARD A. MARTIN, F.G.S. 
ONE’s thoughts travel instinctively to the waters of the ocean when mention is made of waves, and 
it seems at first sight to be a contradiction of terms to associate waves with sand. But one quickly 
realizes that a sea-wave does not necessarily involve a transportation of water, and that the water 
of a wave may itself be stationary, since only the energy which passes through it is translated. 
One then sees that waves can take place in other media than water. The water in a water-wave 
has, however, a movement in a vertical direction, and a wave in a cornfield has an oscillating forward 
and backward movement within certain limits. But in the latter case no one supposes for a moment 
that the ears of corn pass from one side of a field to another, although one can see the wave-impression 
do so. It is when sea-waves approach a coast that there is an actual translation of the water itself, 
and the forward movement of energy dashes the last breaker which is conveying it with a thunderous 
roar upon the strand. 
As water-waves are waves of the wind, so sand-waves are begotten of the wind also. Take a 
smooth water-surface or a smooth sand-surface and let a puff of breath impinge upon either. There 
is immediately a derangement of the surface, even though the current of air be parallel to it, for 
even then friction will do its work. But let a gust of air beat upon it at an angle, and a depression 
is immediately formed, and when a depression is formed, a corresponding ridge must be also formed. 
But the similarity of the two cases ceases here. In water a series of ripples is formed by a single 
