CHAP, iv.] ELECTRICITY AND MAGNETISM. 211 



the unit of time. Hence we say that these abstract equations 

 express the "dimensions" of those quantities with respect to the 

 fundamental quantities length and time. A little consideration 

 will show the student that the following will therefore be the 

 dimensions of the various units mentioned above : 



The "dimensions" of magnetic units are given in the note on 

 Magnetic Units, Art. 324. 



, 



LESSON XXI. Electrometers.^ 



259. In Lesson II. we described a number of electro- 

 scopes or instruments for indicating the presence and 



