80 



Messrs. Ayrton, Mather, and Sumpner 



aluminium wire, to which is screwed the aluminium bridge 

 A A (fig. 11), supporting the needles, carries on one side 



Fig. 11. 



Plan of Ballistic Galvanometer. 



of its lower end a concave mirror (fig. 12) to produce 

 a spot of light on a scale, and on its other side a truly 

 plane mirror, to be viewed with a telescope, if desired. 

 At its lower end it carries a small magnetic needle, w, 

 to be acted on by a pair of coils, 0, joined up in series 

 and having their ends led to the terminal screws, s, s. 

 These coils are quite independent of the main coils of 

 the instrument, and are employed for damping the oscil- 

 lations of the suspended system. With ballistic galvanome- 

 ters previously made for us we have not had any such 

 damping-coil attached : but since to all our galvanometers 



