754 REPORT—1890. 
had currents induced in it-—z.e., I have assumed that the body can be brought up 
as an imperfect conductor and then changed into a perfect conductor i situ. As 
the effect of a magnetic pole is to induce in a perfect conducting plane sheet 
currents which can be magnetically represented by a pole at the reflection of the 
first pole in the sheet, it follows that with a perfect conducting sheet there would 
be no action, such as in Arago’s experiment prevents motion of the sheet parallel 
to itself. There would, no doubt, be a gradual radiation of the energy due to the 
varying magnetic fields. This would have a damping effect on the vibrations, 
much the same as would result from resistance in the conductor. If there were a 
constant force like gravity acting, the equilibrium might exist only for the radiation 
of energy. There is no very great difficulty in calculating the conditions for 
vibrational and logarithmic motions respectively. 
The system is interesting as an illustration on a large scale of how meteoric 
swarms have their energy gradually frittered away into electromagnetic radiations, 
13. On Electrical Oscillations in Air.! By J. TROWBRIDGE. 
14. On the Electrostatic Forces between Conductors and other matters im 
connection with Electric Radiation.2 By Professor Outver J. Lopes, 
F.R.S. 
The author gives an account of an investigation into the forces between electric 
resonators as examined experimentally by Boys, and therefrom branches out into 
several allied subjects connected with the mechanical forces of electric pulses and 
waves. 
WEDNESDAY, SEPTEMBER 10. 
The following Papers were read :— 
1. On Atom-grouping in Orystals (with exhibition of a Model). 
By W. Bartow. 
After referring to some comments made by Sir William Thomson and Professor 
Sohncke on a paper on the same subject read by the author at the Aberdeen 
Meeting of the Association in 1885,° the author stated one of the objects of the 
present paper to be to call attention to some interesting properties of the simpler 
kinds of symmetrical grouping of points, and to an easy method of studying them 
by means of the model exhibited. 
He then described the model as consisting of parallel equi-distant planes of 
homogeneously distributed points (réseaux) represented by beads, and furnished 
with an appliance for simultaneously moving the planes nearer together or further 
apart, while still keeping them equidistant. 
He pointed out that if a series of similar triangularly arranged plane systems 
are so placed in the model, and the distances between the planes so chosen that 
the assemblage of points has the grouping of the cubic system, of which we have 
an example in the arrangement of the centres in a triangular stack of cannon-balls,* 
1 The paper is printed in full in the Proceedings of the American Academy of 
Arts and Sciences, vol. xxv. (N.S. xvii.) 
2 The paper appears in the Philosophical Magazine for September 1890. 
8 See ‘On the Constitution of Matter,’ by Sir William Thomson, Proceedings 
Royal Society of Edinburgh, 1889, pp. 712, 715, 716, and ‘ Erweiterung der Theorie 
der Krystallstruktur,’ von Dr. Leonhard Sohncke, Zeitschrift fiir Krystallographie, 
&e., xiv. 5, pp. 429, 430, 433, 443. 
“See paper read by the author in 1885, published in the Chemical News of 
January 1 and 8, 1886. 
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