6 PBEFACE. 



to self-confidence. Although the following pages 

 record many mistakes made by men of science, 

 they nevertheless show that the true interpreters of 

 nature's laws have nearly always been those who 

 have given some branch of science long and earnest 

 study. It is easy to understand almost any princi- 

 ple of science, but it often requires years of patient 

 eilort to discover and demonstrate a simple natural 

 law. We need to know who the original workers 

 are, and who are best informed on all scientific sub- 

 jects. It is because we do not always know whose 

 opinions are most to be relied upon that erroneous 

 beliefs remain so long among us. Nor can it be 

 said that the educated always fulfil their whole duty 

 in rendering information accessible to others. It 

 is to be feared that they sometimes have too little 

 sympathy with those who are unfamiliar with sub- 

 jects to which they themselves have devoted their 

 attention ; and they possibly fail at times to appre- 

 ciate the capacity of every- day people to understand 

 what is called scientific truth. If there should be 

 such an impression in the mind of any teacher who 

 may have occassion to consult this book he will 

 doubtless become convinced by its contents that 

 erroneous theories are often quite as complicated 

 and difficult of comprehension as the average pro- 

 positions of science. Nothing is more true than 

 that every healthy mind seeks for an explanation of 



