470, 
by Major MacMahon on ‘Partitions of 
Numbers;’ by J. C. Glashan on the ‘ Quin- 
quisection of the Cyclotomic Equation,’ 
and by Dr. Larmor on ‘Jacobi’s Last Multi- 
plier.’ 
On Tuesday the section divided along 
the lines of Electricity and General Phy- 
sics, and many members regretted that they 
were unable to be present in both sections 
simultaneously. In the electrical depart- 
ment there were a number of papers on 
electrical waves and oscillations of differ- 
ent forms. Professor Braun showed how, 
by the action of a magnet on a small pen- 
cil of cathode rays directed on to a fluores- 
cent screen, it was possible to demonstrate 
the form of the wave, either by developing 
the oscillating line of light into a curve 
with the aid of a revolving mirror or by 
using a second magnet to give the corre- 
sponding Lissajou figure. The frequency 
of the coil used was not, however, suitable 
to show the effects in a sufficiently clear 
manner to an audience. Professor Rosa 
exhibited an extremely ingenious mechan- 
ism for automatically plotting the form of 
an alternate current wave by the periodic 
contact method. At each point of the 
cycle the instantaneous difference of poten- 
tial to be measured was found by shifting a 
contact point on a potentiometer wire till 
the galvanometer indicated a balance. On 
depressing a key the point so found was 
recorded on a cylinder, which was moved 
forward automatically in step with the 
periodie contact brush on releasing the 
key. By this means from twenty to thirty 
points could be recorded in a minute. The 
curves exhibited showed in a very remark- 
able manner small waves due to armature 
teeth and commutator segments, which 
could not be obtained with any slower 
method, owing to the necessarily limited 
number of points. Taking special precau- 
tions to secure very steady running of the 
machines, he had been able to analyze these 
SCIEN CE. 
(N.S. Von. VI. No. 143. 
curves with great accuracy as far as the 
fifteenth term of the harmonic series. 
W. D. B. Duddell exhibited an instru- 
ment of a totally different character which 
could be applied to secure instantaneous 
photographs of the forms of these curves 
even under conditions of rapid change such 
as occur in studying the alternate current 
are. He had succeeded in so reducing the 
period and adjusting the damping of a gal- 
vanometer with a pair of strips stretched 
between the poles of an electro-magnet and 
immersed in oil, on the plan suggested by 
Ayrton and Mather, that he was able to ob- 
tain very beautiful records of current and 
potential simultaneously at the ordinary 
rates of alteration on a falling plate. So 
far as could be judged from an inspection 
of the numerous specimens shown, the effect 
of inertia was practically eliminated. It 
would not, of course, be possible to meas- 
ure the these curves with the same degree 
of accuracy as those obtained by the point- 
to-point method, but instantaneous photo- 
graphs can be secured in cases where the 
slower method would be totally inappli- 
cable. 
After the reading of the Report of the 
Committee on Electrical Standards, to 
which reference has already been made, 
Professor J. V. Jones explained a method 
of calculating the coefficient of mutual in- 
duction of a circle and co-axial helix, by 
which the labor may be considerably short- 
ened. ‘This calculation is required in the 
Lorenz method of determining the ohm. 
Professor Ayrton next gave an account of 
the experiments in which he had been en- 
gaged with Professor Jones in redetermin- 
ing the ohm by means of the Lorenz appa- 
ratus constructed for Professor Callendar, 
of McGill University. This apparatus has 
been made by Nalder Brothers, under the 
personal supervision of Professor Jones, 
and is considered to be the most perfect ap- 
paratus of its kind. The value found for 
