192 DISCOURSE ON THE STUDY 



intimate structure on which depend its colour, its 

 hardness, and its chemical properties, remains still 

 concealed : we do not seem to have made even an 

 approach to a closer analysis of it by any such 

 scrutiny. 



(203.) On the other hand, the mechanism of the 

 great system of which our planet forms a part 

 escapes immediate observation by the immensity of 

 its scale, nay, even by the slowness of its evolutions. 

 The motion of the minute hand of a watch can 

 hardly be perceived without the closest attention, 

 and that of the hour hand not at all. But what are 

 these, in respect of the impression of slowness they 

 produce in our minds, compared with a revolving 

 movement which takes a whole year, or twelve, 

 thirty, or eighty years to complete, as is the case 

 with the planets in their revolutions round the sun. 

 Yet no sooner do we come to reflect on the linear 

 dimensions of these orbs, (which however we do 

 not see, nor can we measure them but by a long, 

 circuitous, and difficult process,) than we are lost in 

 astonishment at the swiftness of the very motions 

 which before seemed so slow.* The motion of the 

 sails of a windmill offers (on a small scale) an illus- 

 trative case. At a distance the rotation seems slow 

 and steady but when we stand close to one of the 

 sails in its sweep, we are surprised at the swiftness 

 with which it rushes by us. 



* " When we are told that Saturn moves in his orbit more 

 than 22,000 miles an hour, we fancy the motion to be swift ; but 

 when we find that he is more than three hours moving his own 

 diameter, we must then think it, as it really is, slow." Thirty 

 Letters on various Subjects, by William Jackson, 1 795. 





