1894.] 



on the Work of Hertz. 



331 



now demonstrate. An arc is started directly the large Hertz vibrator 

 is excited at a distance. 



There are some who think that lightning flashes can do none of 

 these secondary things. They are mistaken. 



On the table are specimens of various emitters and receivers such 

 as have been used by different people ; the orthodox Hertz radiator 



Fig. 11. 



A Dumb-bell Form of Radiator. 



of dumb-bell type, Fig. 5, and the orthodox Hertz receivers : — a 

 circular ring, Fig. 6, for interference experiments, because it is but 

 little damped, and a straight wire for receiving at a distance, because 

 it is a much better absorber. Beside these are the spheres and ellip- 

 soids (or elliptical plates), which I have mainly used, Fig. 19, because 

 they are powerful radiators and absorbers, and because their theory 



Fig. 12. 



Dr. Lodge's Hollow Cylindrical Radiator, arranged horizontally against the 

 outside of a metal-lined box. Half natural size. Emitting 3-inch waves. 



has been worked out by Horace Lamb and J. J. Thomson. Also 

 dumb-bells, Fig. 11, without air-gap, and many other shapes, the 

 most recent of mine being the inside of a hollow cylinder with sparks 

 at ends of a diameter, Fig. 12 ; this being a feeble radiator, but a very 



