104 TRANSACTIONS OF THE | JAN. 16, 
to the end of an exposure, hence, the same calculation, perhaps, 
applies. ‘Chis is about the arrangement in a camera I have used 
Fia. 4. 
a great deal, and the exposure so calculated, the 45 of a second 
is nbout my slowest average instantaneous exposure. 
In the following table the information afforded by the film, 
Fig. 2, is condensed. 
Slow shutter, 0.8 cm. headway. Rate of fork, 331.25 vibra- 
tions per second, at ‘I’. 23°C. Variation, about ;3; vibrations 
per degree. 
Film shows 7 vibrations to 4.75 cm. 4.75 vibrations to 3.81 
Tf i 
= — of a second. Velocity of shutter = 47 x 
B9L.25 “4G 
4.75 i 
4.75 = 2,132 metres per second. = — of a second ex- 
331.25 70 
posure. 
A railway train at 50 kilometres per hour = 833.33 metres 
per minute, 138.88 metres per second, and 19.8 cm. in +5 of a 
second exposure. The velocity of the shutter is about 4 the 
velocity of the train. 
In the case of a medium exposure with the same shutter the 
film, Fig. 5, is obtained. Between the vertical lines there are 
Fia. 5. 
VV 
51 undulations, and in the middle 3.81 cm. there are 3.75 un- 
dulations. These data afford an exposure of 5 of a second, 
during which the railway train moves 15.77 cm., and a shutter 
velocity of 3.048 metres per second, which is about 4 the velocity 
of the train. 
Finally, with the same shutter and a quick exposure, the film, 
