38 



Prof. Tyndall on the Relation of 



swing of the needle could be augmented to 20 degrees. Repe- 

 tition showed no deviation from this result : the saturated air 



Ph 



w- 



00 



tf9;3£3^\^ 



60% 



always augmented the opacity, and the dry air always augmented 

 the transparency of the space between the source and the pile. 



Not only, therefore, have the plates of rock-salt been abandoned, 

 but also the experimental tube itself, the displacement between dry 

 and humid air being effected in the open atmosphere. The experi- 



