FALLACIES OF OBSERVATION. 479 



Other examples, scarcely less striking, are recorded by Mr. Wlicwell,* 

 where imaginary laws of nature have continued to be rcceivcMl as leal, 

 merely becauae no one person had steadily looked at facts which almost 

 every one had the opportunity of obsei-\ing. " A vague and loose 

 mode of looking at facts very easily observable, left men for a long 

 time under the belief that a body ten times as heavy as another falls 

 ten times as fast ; that objects immersed in water are always magnified, 

 without regard to the form of the sui-face; that the magnet exerts an 

 irresistible force; that crystal is always found associated with ice; and 

 the like. These and many other are examples how blind and careless 

 man can be, even in observation of the plainest and commonest ap- 

 pearances ; and they show us tliat the mere facidties of perception, 

 although constantly exercised upon innumerable objects, may long fail 

 in leading to any exact knowledge." 



The influence of a preconceived theory is well exemplified in the 

 superstitions of barbarians respecting the virtues of medicaments, and 

 of charms. The negroes, among whom coral, as of old among oui> 

 selves, is worn as an amulet, affirm, acccording to Dr. Paris, t that its 

 color " is always affected by the state of health of the wearer, it becom- 

 ing paler in disease." On a matter open to universal observation, a 

 general proposition which has not the smallest vestige of truth, is 

 received as a result of experience; the preconceived opinion prevent- 

 ing all observation of such instances as do not accord with it. 



§ 4. For illustration of the first species of non-observation, that of 

 Instances, what has now been stated may suffice. But there may also 

 be non- observation of some material circumstances, in instances which 

 have not been altogether overlooked — nay, which may be the very 

 instances upon which the whole superstructure of a theory has been 

 founded. As, in the cases hitherto examined, a general proposition 

 was too rashly adopted, on the evidence of particulars, true indeed, but 

 insufficient to support it ; so in the cases to which we now turn, the 

 particulars themselves have been imperfectly observed, and the singu- 

 lar propositions upon which the generalization is gi'ounded, or some at 

 least of those singular propositions are false. 



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

 brated phlogistic theory ; a doctrine which accounted for combustion 

 by the extrication of a substance supjjoscd to be contained in all com- 

 bustible matter, and to which the name phlogiston was given. Tlie 

 hypothesis accorded tolerably well with superficial appearances : 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 pro- 

 ducts of combustion. When these were at last noticed and brought 

 into account, it appeared to be an luiiversal law, that all substances 

 gain instead of losing weight by undergoing combustion ; and, after 

 the usual attempt to accommodate the old theory to the new fiict by 

 means of an arbitrary hypothesis (that phlogiston had the cpiality of 

 positive levity instead of gravity), chemists were conducted to the true 



* Wheweli,'.-? Phil of the Inductive Sciences, ij., 203. 

 t Pharmacologia, p. 21 



