109 
Scott Russell’s wave-line curve. The length of a wave in 
open water, measured along its base, seems also to depend 
upon and bear a definite relation to the Avidth of the trough 
between two successive waves. The speed of the waves is 
not so much affected as would naturally be imagined by the 
force of the wind. In a moderate gale they run as fast as in 
a heavy one. It is otherwise with their height. 
Mr. Alfred Brothers read the following Paper “ On an 
Improved Diaphragm for determining the Magnitudes of 
Stars.” 
At a recent Meeting of this Society, when Mr. Baxendell 
made a communication respecting one of the variable stars 
of small magnitude, it occurred to me that the system used 
by him for determining the variability of the smaller stars, 
must be not only tedious but often unsatisfactory, owing to 
the necessity for leaving the position of observation for the 
purpose of changing the diaphragms. 
When apertures of various diameters are used as diaphragms, 
placed at the end of the dew-cap of large telescopes, and par- 
ticularly refractors, it must at all times be difficult to make 
these changes, even when the advantage of clock-work motion 
is available; but, with telescopes whose motions must be con- 
trolled by hand, the possibility of determining with accuracy 
such results as the one-tenth of a magnitude must be very 
uncertain; as, unless an assistant be at hand to change the 
diaphragms during the observation, the observer must be 
constantly liable to lose the star at the moment it becomes 
necessary that it should be in the centre of the field of view, and 
the eye in position to note the effect produced by the decrease 
of light on the change of diaphgram being effected. Several 
contrivances have been adopted to contract the aperture of the 
telescope, such as square and hexagonal forms, opened and 
closed mechanically; but hitherto, it is believed, no attempt 
has been made to retain the circular form of aperture. 
