528 
not existed. 
(3) For light buildings, especially if erected on 
soft ground, where the range of motion is always great, if the 
structure rests on layers of fine cast-iron shot, it cannot possibly 
receive the same momentum as a building attached to the moving 
ground. To resist the effects of momentum which cannot be cut 
off a building : (1) Bear in mind the fact that it is chiefly stresses 
and strains which are applied horizontally to a building which 
have to be encountered. A vertical line of openings like doors 
or windows in a building constitute a vertical line of weakness 
to horizontally-applied forces. (2) Avoid coupling together two 
portions of a building which have different vibrational periods, 
or which from their position are not likely to synchronise in 
their motion. If such parts of a building must of necessity be 
joined, let them be so joined that the connecting link will force 
them to vibrate as a whole, and yet resist fracture. Brick 
chimneys in contact with the framing of a wooden roof are apt 
to be shorn off at the point where they pass through the roof. 
Light archways connecting heavy piers will be cracked at the 
crown. To obviate destruction due to these causes a system of 
construction similar to that to be seen in several of the buildings 
of San Francisco, Tokio, and Yokohama may be adopted. This 
essentially consists of tieing the building together at each floor 
with iron and steel tie-rods crossing each other from back to 
front and from side to side. (3) Keep the centre of inertia of a 
building or its parts as low as possible. Heavy tops to chimneys, 
heavy copings, and balustrades on walls and towers, heavy roofs 
and the like are all of serious danger to the portion of the struc- 
ture by which they are supported. When the lower part of a 
building is moved, the upper part by its inertia tending to remain 
behind often results in serious fractures. All the chimneys in 
Tokio and Yokohama which have fallen in consequence of their 
ornamental heads have been replaced by shorter and thicker 
chimneys without the usual coping. The roof of a portion of 
the Engineering College rests loosely on its walls, and has 
therefore a certain freedom. In Manila many heavy roofs have 
been replaced by roofs of sheet iron. Walls may be lightened 
in their upper parts by the use of hollow bricks. Such vertical 
motion as may exist is also partly obviated by light superstruc- 
tures. Vertically-placed iron tie-rods give additional security. 
If these and other rules which are the result of experiment and 
observation could be adopted in earthquake countries, it is 
certain that the loss of life and property might be greatly 
diminished. 
Earth Tremors and Earth Pulsations.—Notwithstanding 
the untrustworthiness of level observations, they neverthe- 
less have given results of interest. (1) The bubbles from 
time to time move back and forth without apparent reason. 
Considerable changes have sometimes been observed before an 
earthquake. (2) The greatest movement of the bubble of a level 
takes place during the colder part of the year, which is the 
season of earthquakes, and also the season when the barometric 
gradient between Siberia and the Pacific is the steepest. (3) 
The bubble of a level continues to move long after the sensible 
motion of-an earthquake has ceased, enabling us to study the 
slow movements which bring an earthquake to a close. (4) 
When the barometer is very low, as, for instance, during a 
typhoon, the bubble of a level may be distinctly seen to pulsate 
back and forth through a range of about ‘5 mm. In September 
of last year, in conjunction with Mr. W. Wilson, C.E., and Mr. 
Mano, of the Imperial College of Engineering, I carried an 
instrument to the summit of Fujiyama, which is about 12, 365 feet 
in height, where I succeeded after many failures in recording 
automatically earth tremors and earih pulsations. But we were 
unable to remain for more than five days. 
The results of interest connected with these observations 
are :—(1) That the movements on the top of the mountain were 
much greater than those which I usually observe in Tokio. (2) 
The tremors, or slight swing-like movements of the instrument, 
did not necessarily accompany the wind. (3) That during the 
heavy south and south-east gales the direction of displacement 
of the pointer was towards the south-east, which is the same 
result as would be obtained if the bed-plate of the instrument 
were raised on the south-east side, or if the mountain had tipped 
over to the north-west. My colleague, Mr. T. Alexander, 
treating Fuji as a conical solid made of brick, with a wind-load 
of 50 Ibs. on the square fuot, found the slope and deflection of a 
point 100 feet below the apex of the cone. This calculated 
slope was two or three times greater than the greatest deflection 
which I measured. As it is difficult to imagine that a mountain 
could suffer deflection by a wind pressure, I will not insist upon 
NATURE 
[ Oct. 1, 1885 
the fact that deflection actually occurred. It is certainly curious 
that the results of calculation and observation should point 1n the 
same direction. 
Report of the Committee on Electrical Standards, consisting of 
Prof. G. C. Foster, Sir W. Thomson, Prof. Ayrton, Prof. F. 
Perry, Prof. W.G. Adams, Lord Rayleigh, Prof. O. F. Lodge, 
Dr. Fohn Hopkinson, Dr. A. Muirhead, Mr. Preece, Mr. H. 
Taylor, Prof. Everett, Prof. Schuster, Dr. F. A. Fleming, 
Prof. G. F. Fitzgerald, Mr. R. T. Glazzbrook, Prof. Chrystal, 
Mr. H. Tomlinson, and Prof. Barnett, with Mr. Glazebrook as 
Secretary.—The Committee reported that the Secretary has had 
constructed a series of coils to serve as standards in terms of the 
legal ohm. These standards, in accordance with the resolution 
of the Committee, were con-tructed on the supposition that the 
value of the legal ohm is r’o112 B.A. units. The comparisons 
were made by the methods given in the reports for 1885 and 
1884, and the values found were— 
No. Resistance Temperature 
100 999515 I4'I 
101 998845 I4'l 
102 10°00415 16°7 
103 10°00352 16°75 
104 100°0304 16°05 
105 100°0436 16°05 
106 1000°694 17°4 
107 1000°677 17°45 
108 10006°8 17°35 
109 10006°8 17°35 
These standards have also been compared with mercury-tube 
resistances constructed by Mr. Benoit, of Paris, and a difference 
of ‘00049 legal ohm was found. The legal ohm standards, as 
constructed by the Committee, exceed by this amount those 
constructed in Paris. Six coils have been compared with the 
standards during the year, and the values are given. The Com- 
mittee hope that arrangements may be made for issuing standards 
of electromotive force, and for constructing and issuing standards 
of capacity. In conclusion, they ask to be reappointed, with 
the addition of the names of Prof. J. J. Thomson and Mr. W. 
N. Straw, with a renewal of the unexpended grant of 5o0/. 
Report on Electrical Theortes, by Prof. J. J. Thomson.—This 
report deals exclusively with those theories which only profess 
to give mathematical expressions for the forces due to a distribu- 
tion of currents. Those theories which profess to give mechanical 
explanation of these forces are not considered. There was not 
sufficient time to consider both classes of theories, and it is evident 
that the mathematical theory must be settled before we can get 
a satisfactory mechanical one. As to the general result of the 
inquiry, we may say that all that has been proved is that it is 
absolutely necessary to take into account the currents in the 
dielectric ; and that the action of these, as well as other currents, 
must be given by some form of the potential theory—that is, the 
theory propounded by F. E. Neumann and generalised by Von 
Helmholtz. But nothing definite is known as to what we should 
take as the measure of these electric currents, and which of the 
many forms of the potential theory is the right one. We hardly 
require experimental proof that alteration in the polarisation of 
the dielectric, at any rate if the dielectric be other than the 
ether, produce effects analogous to those produced by an ordinary 
current flowing through a conductor. For the polarisation of a 
dielectric by an electromotive force produces a change in the 
structure of the dielectric. This is shown by the alteration in 
volume experienced by glass and other bodies when placed in 
the electric field, and also by the breaking down of the dielectric 
when the strength of the field is great enough. Now, if we 
move a magnet we shall, since we produce an electromotive 
force in its neighbourhood, produce a change in the structure of 
the dielectric around it because we alter its state of polarisation. 
It follows, then, from the principle of action and reaction, that 
if we alter the state of polarisation of the dielectric we shall 
alter the state of motion of the magnet. So that an alteration 
in the polarisation of the dielectric produces a magnetic force. 
We can show in a similar way that an alteration in the polarisa- 
tion must produce all the effects produced by an ordinary con- 
duction current. We know nothing, however, about the mag- 
nitude of the current which is equivalent to a change in the 
state of polarisation. It seems natural to suppose that the in- 
tensity of the current is proportional to the rate of change of 
the electromotive force. Let us suppose that it equals » (rate of 
z — — 
