106 TRANSACTIONS OF THE [JAN. 16, 
is presented the register of a common guillotine shutter, ac- 
tuated by a pair of light rubber bands (No. 33 Faber), and falling 
through a distance of 12.5 cm. 
The acceleration increases to the end of the shutter’s excur- 
sion, although it is restricted in this case by a retarding spring, 
which I omitted to remove, and the rubber bands are so attached 
as to be hardly stretched beyond normal length before the shut- 
ter is set. 
The entire number of undulations is about 12, the opening in 
the shutter is 4.1 cm., twice which linear measure, plus a cor- 
rection for expansion of the film, makes 9.2 cm., which, at the 
middle of the record embraces 7 waves, and gives 7 of a second 
as the time of exposure, for an aperture 4.1 cm. in diameter. If 
it were desirable, the time of this exposure could be reduced by 
so constructing the shutter that its top would run nearly to the 
lens opening and the exposure occur at the last moment. ‘To 
demonstrate experimentally this acceleration, I some time since 
suggested a ribbon shutter, designed to operate with a head- 
way of 50 cm., more or less, before exposure. No experiment 
is now required to assure us of the efficacy of such a shutter. 
More rapid exposures can undoubtedly be secured by in- 
creasing the headway of the shutter, with a given tension, quite 
as advantageously perhaps as by increasing the tension, es- 
pecia ly beyond exposures of the one hundred and fiftieth of a 
second, 
It might be supposed that the acceleration of the large shut- 
ter shown in Fig. 7 A is due in part to gravity. By its side 
(Fig. 7 B) isa record of the same shutter caused to fall (?) up- 
ward by the same spring tension. The difference in length 
arises from the difference in expansion of the films. In the 
number of undulations its upward is, perhaps, not quite the 
same as its downward record, but in the acceleration the two 
are nearly identical. In the British Journal of Photography 
for 1887, page 205, Mr. Richard Parr, reasoning from certain 
experiments, recommends an upward falling shutter as giving 
greater exposure to the foreground and less to the sky. His 
deduction is supported by the graphic evidence herein pre- 
sented, that in ordinary shutters of moderate headway the first 
half of the exposure is longer than the latter half, and that 
even in the more advanced stages of the shutter’s excursion a 
progressive acceleration still occurs. 
In Fig. 8 is presented the record of another shutter. It is 
lighter than the one first used, being made wholly of pasteboard, 
and it was drawn by a thin rubber spring, 9 cm. long, stretched 
in a line with the shutter to 19.1 cm. Our attention is im- 
mediately drawn to the peculiar doubling of the undulating line 
