PREVALENCY OF SOURCES Otf ERROR. 107 



of the various sources and forms of error and fallacy is 

 especially important, because he is extremely apt to be 

 misled by them, and to greatly under-estimate their 

 variety, number, and specious character ; nor can his 

 study of them be commenced too soon, because an error 

 committed, or a fallacy unobserved, in the early part of 

 an original research, is liable to affect seriously all the 

 results, and all the conclusions drawn from them. It is 

 said that the late Mr. Bailey, in his researches on the 

 density of the earth, discovered, after several years of 

 labour and making a multitude of experiments, an error 

 pervading the whole ; and he had to correct the error, and 

 then repeat all of the experiments. 



A single serious error has, in some instances, caused 

 an investigator to abandon science. The following 

 example is given by Dr. Thomson : ' Chenevix was for 

 several years a most laborious and meritorious chemical 

 experimenter. It is much to be regretted that he should 

 have been induced, in consequence of the mistake into 

 which he fell respecting palladium, to abandon chemistry 

 altogether. Palladium was originally made known to the 

 public by an anonymous handbill which was circulated in 

 London, announcing that palladium, or new silver, was 

 on sale at Mrs. Forster's, and describing its properties. 

 Chenevix, in consequence of the unusual way in which 

 the discovery was announced, naturally considered it as 

 an imposition upon the public. He went to Mrs. 

 Forster's, and purchased the whole of the palladium in 

 her possession, and set about examining it, prepossessed 

 with the idea that it was an alloy of some two known 

 metals. After a laborious set of experiments, he con- 

 sidered that he had ascertained it to be a compound of 

 platinum and mercury, or an amalgam of platinum made 

 in a peculiar way, which he describes. The paper was 



