SECTIONAL TRANSACTIONS.—At. 453 
multiply a transformer potential by a factor whose magnitude depends 
simply on the number of condensers and rectifiers employed, the final output 
being a potential hav.ng a ripple of only a few per cent. A tower of glass 
cylinders evacuated by an oil diffusion pump constitutes the four rectifying 
units employed in the 700,000-volt generator at the Cavendish Laboratory. 
The general principles underlying the design of vacuum tubes for these 
voltages are discussed. 
Dr. R. J. vAN DE Graarr.—Engineering possibilities of electrostatics 
with vacuum insulation, 
An electrostatic force requires merely the presence of electric charges, 
whereas an electromagnetic force requires in addition the continuous 
motion of the charge. This movement of the large charges necessary for 
electromagnetic force inevitably causes certain difficulties, fundamentally 
limiting the efficiency, compactness and lightness of electromagnetic 
machinery. These difficulties can be eliminated by the use of electro- 
static rather than the usual electromagnetic force, provided that a suitable 
insulating medium is available for the high voltages and gradients required. 
Certain experimental evidence supports the belief that high vacuum has 
the desired insulating properties, and that it can be suitably produced for 
large electrostatic machinery. Assuming that the above evidence is correct 
in showing that vacuum insulation can be made to prevent electrical break- 
down, designs for electrostatic generators and motors are given, with cal- 
culations showing that they would have a greater power output per unit 
of size and weight, with energy losses many times less than present electro- 
magnetic machinery. 
Prof. W. Cramp.—Axial spin of a magnetic field. 
At the end of the year 1831 Faraday carried out a series of experiments 
upon the effects of the relative motion of a conductor and a magnetic field. 
He concluded that the moving conductor was the seat of the e.m.f., and that 
there was ‘a singular independence of the magnetic field and the bar in 
which it resides.’ Subsequent writers, however, are at variance as regards 
the relationship between a permanent bar magnet and its field, some taking 
the view that when such a magnet is given an axial spin its field moves with 
it, and others that the field is structureless, and that rest or motion as applied 
to it are meaningless. 
In an attempt to resolve this problem, the author has carried out a long 
series of experiments, not only upon conductors and magnets, but also upon 
conductors and solenoids, The results are in some instances unexpected, 
but in general lead to the conclusion that a spinning magnet and a spinning 
solenoid behave in an exactly similar manner, and that in no circum- 
stances can the magnetic field of a cylindrical bar magnet be regarded as 
rotating with the bar in an axial spin. Further, it appears to be impossible 
to cause a turning moment about the axis of such a magnet by means of 
current-carrying conductors lying in its magnetic field. In short, while 
the mechanical effects upon conductors carrying currents and lying in a field 
leave little doubt as to a connection between the current and the material 
of the conductor, there is no evidence of a similar attachment between 
a magnet and its field. 
AFTERNOON. 
Visit to University College, Nottingham. Meeting in Physics Depart- 
ment, with papers by members of the department. 
