DOVE ON THE ELECTRICITY OF INDUCTION. 187 



6. The current of Saxton's machine with an empty wire 

 keeper. 



7. The current of the same machine with a surrounded iron 

 keeper. 



8. The current of the closed thermo- or hydro-circuit. 



In the history of the science, the first and last members of 

 this series were the first to be discovered. Such a wide gap lay 

 between them that doubts were entertained as to their identity. 

 Now that a number of intermediate members have been supplied 

 by the phaenomena of induction, the gradation has become so 

 gentle, that any endeavour to draw a line of demarcation between 

 them must be perfectly arbitraiy. 



