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Profs. W. E. Ayrton and J. Perry. [Feb. 14, 



of charcoal iron attached at its lower end to a brass piece Gr guided 

 at the bottom in the way shown. To Gr is attached the lower end 

 of a spring made in the way we have described of silver or hard 

 phosphor-bronze, the upper end of which is attached rigidly by a thin 

 rod to the glass top of the instrument which itself is fastened rigidly 



to the framework of the instrument. The rod attached to the glass, 

 and to which the upper end of the spring is attached, also serves as a 

 guide to the top of the iron tube. In the space FF a solenoid wire or 

 strip is wound, its ends being attached to the terminals shown. Hence 

 when a current is passed through the wire, the iron tube is sacked 

 into the solenoid, and its lower end G, to which the spring is attached, 

 receives a large rotatory motion, which is communicated directly to 

 the pointer attached to the top of the iron tube. Parallax in taking 



