While composing a little treatise on Eternity, I had the curiosity to place a mirror before me; and ere long saw reflected there, a curious involved worming and undulation in the atmosphere over my head.
North of the Congo basin and separated from it by a broad undulation of the surface is the basin of Lake Chad - a flat-shored, shallow lake filled principally by the Shari coming from the south-east.
Several pretty large logs may still be seen lying on the bottom, where, owing to the undulation of the surface, they look like huge water snakes in motion.
His powerful scientific imagination enabled him to realize that all the points of a wavefront originate partial waves, the aggregate effect of which is to reconstitute the primary disturbance at the subsequent stages of its advance, thus accomplishing its propagation; so that each primary undulation is the envelope of an indefinite number of secondary undulations.
Climatic agencies have smoothed and modified everything rugged or abrupt, until an impression of gentle undulation rather than of grandeur is suggested.