ON TERRESTRIAL SURFACE WAVES AND WAVE-LIKE SURFACES. 301 
Terrestrial Surface Waves and Wave-like Surfauces.—Fourth Report of 
the Committee, consisting of Dr. J. Scorr Kent (Chairman), 
Dr. VauGHAN CornisH (Secretary), Lieut.-Col. F. BatLey, Mr. 
JOHN MILNE, and Mr. W. H. WHEELER. (Drawn up by the 
Secretary.) 
[PLATE VII.] 
Tue Committee record with deep regret the death of Mr. E. A. Floyer, 
M.R.A.S., Mem. Inst. Egypt, a Member of this Committee, who was 
especially interested in the study of desert sand-dunes. A list of his 
principal writings upon this and other subjects, compiled by Dr. Cornish, 
has appeared in the ‘Journal of the Royal Asiatic Society,’ May 1904.! 
In the last report some account was given of observations upon the 
Bore of the river Severn, and of the waves in the Whirlpool Rapids of 
Niagara River. Further observations upon waves in rivers and upon 
kindred phenomena in waterfalls were commenced in May last in 
Switzerland, as well as observations upon Steps and Ledges produced by 
the Movement of Soil upon a Slope. The work is still in progress, but a 
preliminary account may here be given of one kind of wave of special 
interest now being kept under observation in the Guntenbach and 
Griinnbach streams, which flow in the latter part of their course in open 
paved conduits into the Thunersee. Each terminates in a_ waterfall 
which is not steady, nor merely flickering, but is affected by a regular 
cadence having a period of several seconds. In the case of the Griinnbach 
the phenomenon is easily visible at the distance of a mile with the naked 
eye. The amount of water at maximum is fully one-third greater than 
at minimum. This cadence is due to the arrival of waves resembling a 
bore, but travelling down channel more rapidly than the current flows. 
These it is proposed to call Roll Waves, from a name which a correspon- 
dent gives to a wave of similar form which sometimes occurs in the river 
Tees. Itis the form, as far as can be judged by written and verbal 
accounts unaccompanied by photographs, in which sudden floods some- 
times travel down a river, as in the recent destructive flood at Nikko, 
Japan. The remarkable thing about these waves in the Guntenbach and 
Griinnbach, however, is their periodicity, and the fact that they are 
spontaneously evolved without the co-operation of any special quickening, 
or checking, or sudden swelling of the current. They appear to depend 
mostly upon the shallowness of the stream (and therefore require a fairly 
smooth bottom), in conjunction probably with considerable swiftness. 
The ordinary quick throbbing of the current (to which the present writer 
has often referred) gives rise in these very shallow streams to ‘long 
waves’ whose amplitude is an appreciable fraction of the depth of the 
stream. The greater of these, therefore, move more rapidly than those of 
lesser amplitude, and can actually be seen to catch them up. They do 
not, however, pass them by, but, on the contrary, incorporate them; and 
thus the original small, rapid, irregular throb of the stream is changed, as 
the stream flows on, into a slow and nearly regular cadence. The period 
becomes longer and more regular in the lower reaches of the conduits, as 
can best be observed in the Griinnbach, of which the conduit is longer and 
* Dr, Cernish’s completed paper ‘On the Dimensions of Deep-sea Waves and their 
Relation to Meteorological and Geographical Conditions’ has appeared in the 
Geographical Journal for May 1904. 
