A WORD TO THE READER 19 



There is a great amount of litera- 

 ture on the subjects treated in these 

 volumes, and I have a library of more 

 than a thousand books on this and kin- 

 dred subjects, most of them being 

 theoretical only, or compilations rather 

 than records of "actual experimental 

 work. 



This work, if carried on extensively, 

 requires constant daily and hourly at- 

 tention, and these volumes have been 

 mostly written on paper pads during the 

 occasional wakeful hours of night, with- 

 out light, and of course without use of 

 my eyes, which have always been too 

 much occupied with experiments while 

 daylight lasted. Notwithstanding the 

 fact that those who are making history 

 seldom have time to record it, these 

 records have been made for the benefit 

 of those who follow, and it is hoped that 

 this partial description of actual, vital, 



