http://www.allaboutcircuits.com/vol_1/chpt_1/1.html
"Charles Dufay was one the early experimenters [...]"

probably should be:
"Charles Dufay was one of the early experimenters [...]"

 

. Charles Dufay was one the early experimenters who demonstrated that there were definitely two

Yup, its a typo.

 

Thanks for pointing out this error. I have changed the copy at ibiblio to reflect this correction.

Dennis Crunkilton