60 



Captain W. de W. Abney 



[March 17, 



bromide ; an exposure of twenty seconds will suffice to impress the 

 image of the points by their dark rays. [The image was developed 

 and subsequently shown.] It will be seen that the bromide in this 

 state is somewhat sluggish to respond to the vibiations of the dark 

 rays. I will now make an experiment to show how different is 

 the behaviour of the orange bromide. Behind this rotating disc, 



Fig. 2. 



5 



?.3 



fPi?fi^ 



1000 



10000 



iOtti 



8009 



7009 



6 000 



fSCCO 



rtismatic Solar Spectrum, 

 Moasurod from a. PbetogrOfi , 



which is made up of alternate transparent and oj^aque sectors, is 

 a plate prepared with the orange bromide. A spark i of an inch 

 in length from a battery of Leyden jars is sufficient to impress 

 a sharp image of the sectors on the plate though they are rapidly 

 rotating. [The exjwsure was made to the spark whilst the disc 



