Sentence:  Each frame comes between the light and the lens and is individually projected on the screen , at the rate , for silent movies , of 16 frames per <WSD>second</WSD> , and , for sound films , 24 frames per second . 
Meaning of the word marked with <WSD> tags:  1/60 of a minute; the basic unit of time adopted under the Systeme International d'Unites