SCIENTIFIC SIDE-LIGHTS 



1. ABERRATION OF LIGHT Apparent 

 Motion of Stars in Space Due to Motion of 

 the Earth. Bradley . . . noticed that 

 the fixed stars did not really appear to be 

 fixed, but that they describe little orbits in 

 the heavens every year. The result per- 

 plexed him. . . . He was one day upon 

 the Thames in a boat, and noticed that as 

 long as his course remained unchanged, the 

 vane upon his masthead showed the wind to 

 be blowing constantly in the same direction, 

 but that the wind appeared to vary with 

 every change in the direction of his boat. 

 " Here," as Whewell says, " was the image 

 of his case. The boat was the earth, mov- 

 ing in its orbit, and the wind was the light 

 of a star." . . . You will immediately 

 understand the meaning of Bradley's dis- 

 covery. Imagine yourself in a motionless 

 railway-train, with a shower of rain de- 

 scending vertically downwards. The mo- 

 ment the train begins to move the rain- 

 drops begin to slant, and the quicker the 

 motion of the train the greater is the 

 obliquity. In a precisely similar manner 

 the rays from a star vertically overhead are 

 caused to slant by the motion of the earth 

 through space. Knowing the speed of the 

 train, and the obliquity of the falling rain, 

 the velocity of the drops may be calculated; 

 and knowing the speed of the earth in her 

 orbit, and the obliquity of the rays due to 

 this cause, we can calculate just as easily 

 the velocity of light. TYNDALL Lectures on 

 Light, lect. 1, p. 22. (A., 1898.) 



2. ABRASION OF ROCKS BY GLACIERS 



Marks of Ice That Melted Ages Ago. In 

 the first place, we have to consider the sin- 

 gular abrasion of the surfaces over which 

 the glacier has moved, quite unlike that pro- 

 duced by the action of water. We have seen 

 that such surfaces, wherever the glacier- 

 marks have not been erased by some subse- 

 quent action, have several unfailing charac- 

 teristics : they are highly polished, and they 

 are also marked with scratches or fine strice, 

 with grooves and deeper furrows. Where 

 best preserved, the smooth surfaces are shin- 

 ing; they have a luster like stone or marble 

 artificially polished by the combined friction 

 and pressure of some harder material than 



itself until all its inequalities have been 

 completely leveled and its surface has be- 

 come glossy. Any marble mantelpiece may 

 serve as an example of this kind of glacier- 

 worn surface. AGASSIZ Geological Sketches, 

 ser. ii, p. 34. (H. M. & Co., 1896.) 



3. Rocks Are Cut by Exist- 



ing Glaciers. At the lower end, and along 

 the sides of many Alpine glaciers, the ice 

 charged with sand and stones may be seen 

 in direct contact with the smooth, polished, 

 and striated rock surfaces. Below glaciers 

 that have recently retreated, and where the 

 surface is still bare of vegetation, records 

 similar to those just mentioned may be ob- 

 served in thousands of localities. The same 

 is true, also, over vast regions that are 

 known to have been formerly glaciated; 

 while on adjacent areas, where the condi- 

 tions are similar, excepting that they were 

 not occupied by ice, the peculiar and not 

 easily mistaken evidences of ice abrasion 

 are lacking. We have, therefore, both posi- 

 tive and negative evidence pointing to the 

 conclusion that glaciers abrade the rocks 

 over which they flow. RUSSELL Glaciers of 

 North America, int., p. 19. (G. & Co., 

 1897.) 



4. ABSENCE OF MIND Newton and the 

 Egg. Always preoccupied with his pro- 

 found researches, the great Newton showed 

 in the ordinary affairs of life an absence of 

 mind which has become proverbial. It is re- 

 lated that one day, wishing to find the num- 

 ber of seconds necessary for the boiling of 

 an egg, he perceived, after waiting a minute, 

 that he held the egg in his hand, and had 

 placed his seconds watch (an instrument of 

 great value on account of its mathematical 

 precision) to boil! FLAMMARION Popular 

 Astronomy, bk. ii, ch. 1, p. 93. (A.) 



5. ACCIDENT CONFIRMS SUPERSTI- 

 TION Indian's Prognostication of Calamity 

 A Hunter's Omen. The effect of accidental 

 occurrences upon an uneducated mind, in 

 engendering superstition, is a subject which 

 has often been dwelt upon, and the diffi- 

 culty of eradicating the same as may be 

 judged of by the following accident which 

 came under the observation of Mr. T. B. 



