THE SIX GATEWA YS OF KNOWLEDGE. 287 



manship. It is bad logic that leads to trusting 

 to the dead-reckoning, in running a course at 

 sea ; and it is that bad logic which is the 

 cause of those terribly frequent wrecks ; of 

 steamers, otherwise well conducted, in cloudy but 

 perfectly fine weather running on rocks at the 

 end of a long voyage. To enable you to under- 

 stand precisely the meaning of your result when 

 you make a note of anything about your own 

 experience or experiments, and to understand 

 precisely the meaning of what you write down, 

 is the province of logic. To arrange your record 

 in such a manner that if you look at it after- 

 wards it will tell you what it is worth, and 

 neither more nor less is practical logic ; and if 

 you exercise that practical logic, you will find 

 benefits that are too obvious if you only think 

 of any scientific or practical subject with which 

 you are familiar. 



There is danger then of a bad use of words, and 

 hence of bad reasoning upon them, in speaking 

 of light and radiant heat ; but if we distinctly 

 define light as that which we consciously perceive 



