OF NATURAL PHILOSOPHY. 121 



pressions of facts, we must take care, in observing, 

 to have them all in activity, and to let nothing escape 

 notice which affects any one of them. Thus, if 

 lightning were to strike the house we inhabit, we 

 ought to notice what kind of light we saw whether 

 a sheet of flame, a darting spark, or a broken zig-zag; 

 in what direction moving, to what objects adhering, 

 its colour, its duration, &c. ; what sounds were 

 heard explosive, crashing, rattling, momentary, or 

 gradually increasing and fading, &c. ; whether any 

 smell of fire was perceptible, and if sulphureous, 

 metallic, or such as would arise merely from sub- 

 stances scorched by the flash, &c. ; whether we felt 

 any shock, stroke, or peculiar sensation, or expe- 

 rienced any strange taste in our mouths. Then, 

 besides detailing the effects of the stroke, all the 

 circumstances which might in any degree seem 

 likely to attract, produce, or modify it, such as 

 the presence of conductors, neighbouring objects, 

 the state of the atmosphere, the barometer, ther- 

 mometer, &c., and the disposition of the clouds, 

 should be noted; and after all this particularity, 

 the question how the house cawe to be struck 9 might 

 ultimately depend on the fact that a flash of light- 

 ning twenty miles off passed at that particular 

 moment from the ground to the clouds, by an effect of 

 what has been termed the returning stroke. 



(113.) A writer in the Edinburgh Philosophical 

 Journal* states himself to have been led into a series 

 of investigations on the chemical nature of a peculiar 

 acid, by noticing, accidentally, a bitter taste in a 



* Edinburgh Phil. Journ. 1819, vol. i. p. 8. 



