172 ANNUAL OF SCIENTIFIC DISCOVERY. 



circular waves, which, after reflection, again encircle the centre. If the point 

 of disturbance be a little removed from the centre, the intersections of the 

 direct and reflected waves produce magnificent chasing. The luminous 

 figure reflected from such a surface is exceedingly beautiful. When the 

 mercuiy is lightly struck by a glass point, in a direction concentric with the 

 circumference of the vessel, the lines of light run round the vessel in mazy 

 coils, interlacing and unravelling themselves in the most wonderful manner. 

 If the vessel be square, a splendid mosaic is produced by the crossing of the 

 direct and reflected waves. Description, however, can give but a feeble idea 

 of these exquisite effects. Professor Tyndall. 



ON THE DESTRUCTIVE EFFECTS OF WAVES. 



Mr. Thomas Stevenson, C. E., in a communication to the Royal Society 

 of Edinburgh, states that he had found on one of the Shetland Islands, 

 exposed to the waves of the North Sea, or German Ocean, masses of rock 

 weighing nine and a half tons and under, heaped together by the action of 

 the waves, at the level of no less than sixty-two feet above the sea; and 

 others, ranging from six to thirteen tons, were found to have been quarried 

 out of their positions in situ, at levels of from seventy to seventy-four feet 

 above the sa; another block, of seven and one-sixteenth tons, at the level 

 of twenty feet above the sea, had been quarried out and transported to a 

 distance of seventy-three feet, from S.S.E. to N.N.W., over opposing abrupt 

 faces as much as seven feet in height. 



Mr. S. further stated that, as the result of observation, he was of the 

 opinion that the presence of mud on the sea bottom, at any depth, might be 

 taken as a certain proof that the agitation originating at the surface had 

 ceased to be appreciable. If the geological formation did not produce a 

 clayey deposit, or if strong submarine currents existed, the absence of mud 

 might afford no proof of the magnitude of the waves ; but its presence in shoal 

 water may be relied on as indicating with certainty that, in whatever locality 

 it is found, there must be small disturbance at the surface, or, in other words, 

 that there cannot be a heavy sea. 



SEEING THE EARTH'S ANNUAL MOTION. 



The pendulum experiment of Mr. Foucault, by which the diurnal motion 

 of the earth was made visible, has been followed by a contrivance of M. 

 Fitzeau, to exhibit the annual motion, which cannot, however, be of so 

 popular a character; nor does it admit of simple explanation. By directing 

 a telescope east and west at the time of the solstices, and viewing the rota- 

 tion of the plane of polarization of a ray of light by means of a special 

 apparatus which it contained, he observed a small movement, only to be 

 accounted for by the annual motion of the earth. 



Seeing the Earth's Diurnal Motion. M. Perrot, of Paris, exhibits the diur- 

 nal motion of the earth by means of a bucket, with a small hole exactly in 

 the centre of its bottom. The bucket is filled with water and some light 

 powder strewn upon its surface, which shows the direction of the current 

 produced by the escape of the water through the orifice described. This 

 current is seen to follow a curve considerably to the right of the straight 

 line it would take if the earth were standing still, and which is accounted 

 for by its rotation. The action of the earth's rotation, he thinks, is also 



