98 KNOWLEDGE AND OPINION. 



toughest metal I The wliole world around us 

 exists in virtue of the helief in science — tliat is 

 to say, in ascertained fact. If we were all to 

 refuse belief in the laws of physics, we should 

 walk over precipices and get dashed to pieces on 

 the ground beneath ; if we were all to refuse 

 belief in the laws of chemistry and electricity, we 

 might go back to tallow candles and weekly posts. 

 Why, we should not be able to have even these ; 

 for to light a candle with a match implies belief 

 in ever so many scientilic truths — that matches 

 ignite when struck ; that wicks can be set on fire 

 by lighted m itches; that candles will burn slowly 

 and give out sensible light; and so forth ad 

 infinitum. 



How is it, then, that scientific men seem always 

 to be at loggerheads with one another about the 

 principles of their own sciences? The answer is, 

 because their chief interest at any moment is con- 

 centrated upon what may be called the growing- 

 point of their subject — the small part that is just 

 passing from the stage of mere ojjinion or suspi- 

 cion into the stage of ascertained fact. In astron- 

 omy there is a vast body of certain and fixed 

 truths about the sun, the planets, the comets, the 

 meteors, the fixed stars, the great cloudy, hazy 

 masses which we call the nebulae. These truths 

 nobody doubts; and astronomers, therefore, are 

 not greatly engaged in discussing them. They 



