348 FALLACIES. 



Such, for instance, was one of the mistakes committed in 

 the celebrated phlogistic theory ; a doctrine which accounted 

 for combustion by the extrication of a substance called phlo- 

 giston, supposed to be contained in all combustible matter. 

 The hypothesis accorded tolerably well with superficial appear- 

 ances : the ascent of flame naturally suggests the escape of a 

 substance; and the visible residuum of ashes, in bulk and 

 weight, generally falls extremely short of the combustible 

 material. The error was, non-observation of an important 

 portion of the actual residue, namely, the gaseous products of 

 combustion. When these were at last noticed and brought 

 into account, it appeared to be an universal law, that all sub- 

 stances gain instead of losing weight by undergoing combus- 

 tion; and, after the usual attempt to accommodate the old 

 theory to the new fact by means of an arbitrary hypothesis 

 (that phlogiston had the quality of positive levity instead of 

 gravity), chemists were conducted to the true explanation, 

 namely, that instead of a substance separated, there was on 

 the contrary a substance absorbed. 



Many of the absurd practices which have been deemed 

 to possess medicinal efficacy, have been indebted for their 

 reputation to non-observance of some accompanying circum- 

 stance which was the real agent in the cures ascribed to 

 them. Thus, of the sympathetic powder of Sir Kenelm 

 Digby: "Whenever any wound had been inflicted, this 

 powder was applied to the weapon that had inflicted it, which 

 was, moreover, covered with ointment, and dressed two or 

 three times a day. The wound itself, in the meantime, was 

 directed to be brought together, and carefully bound up with 

 clean linen rags, but above all, to be let alone for seven days, 

 at the end of which period the bandages were removed, when 

 the wound was generally found perfectly united. The triumph 

 of the cure was decreed to the mysterious agency of the sym- 

 pathetic powder which had been so assiduously applied to the 

 weapon, whereas it is hardly necessary to observe that the 

 promptness of the cure depended on the total exclusion of 

 air from the wound, and upon the sanative operations of 

 nature not having received any disturbance from the officious 



