1878.] 
The British Association . 
519 
lengths corresponding to each position in the spectrum had 
been determined with great care, and these, when corrected 
for the dispersion of the air, were proportional to the cor- 
responding periodic times, which thus become known. By 
a discussion of the observations it might be expedted that 
much will be learned with regard to the original dis- 
turbance caused by the source of light. In the present 
state of science it is of importance to facilitate this inquiry 
as much as possible, and it is hoped that aid will be given 
to the student of Nature by the table published in connec- 
tion with the Report, in which the oscillation-frequencies of 
the principal rays of the visible part of the solar spedtrum 
have been computed from Angstrom’s determinations of 
their wave-lengths in air, combined with Ketteler’s observa- 
tions on the despersion of air. 
Mr. Stoney also read three other papers “ On a Spectro- 
scope of Unusually Large Aperture,” “ On the Support of 
Spheroidal Drops and Allied Phenomena,” and “ On the 
Cause of the Travelling of Spheroidal Drops.” 
Captain Douglas Galton then read a paper “ On some 
Recent Experiments upon the Coefficient of Fridtion be- 
tween Surfaces Moving at High Velocities.” The author 
has recently been engaged in making some experiments in 
connection with the adtion of brakes in use on railways. A 
number of diagrams and tables illustrated the means by 
which the results were obtained, and the principal results 
shown by them maybe summed up as follows: — (1.) The 
application of brakes to the wheels, when skidding is not 
produced, does not appear to retard the rapidity of rotation 
of the wheels. (2.) When the rotation of the wheels falls 
below that due to the speed at which the train is moving, 
skidding appears to follow immediately. (3.) The resistance 
which results from the application of brakes without 
skidding is greater than that caused by skidded wheels. 
(4.) During the movement of skidding the retarding force 
increases to an amount beyond that which prevailed before 
the skidding took place ; but immediately after the aCt of 
skidding is complete, this pressure falls down again to much 
below what it was before the skidding. (5.) The pressure 
required to skid the wheels is much higher than that re- 
quired to hold them skidded, and appears to bear a relation 
to the weight on the wheels themselves, as well as to their 
adhesion and velocity. The general conclusion which 
would appear to follow from the results of the preliminary 
experiments is that none of the hand brakes, and only some 
of the continuous brakes now in use, have been designed 
