48 
IOWA ACADEMY OF SCIENCES. 
spherical surface containing the point; following the law of all 
forces expanding in three- fold space, which may be stated thus: 
Force x area of distribution=a constant. 
From this fact it is evident that the distribution of the force 
of gravitation is confined to threefold space; for, since the 
boundary of a fourfold sphere is a solid, a force expanding in 
all directions from a point in fourfold space decreases in inten- 
sity in proportion to the increase of the boundary, that is to 
say, in proportion to the cube of the radius, instead of follow- 
ing Newton’s law. 
Newton’s law has been experimentally proved for distances 
that are very great compared with the diameter of an atom, and 
to a degree of accuracy limited by errors of experiment. It 
does not necessarily follow that the law holds with absolute 
accuracy, or that it holds at all for distances comparable with 
atomic dimensions. All that we can say is that for distances 
moderate and great the law expresses the facts as accurately 
as they have been experimentally determined. 
Gravitation is not, like magnetism, polar. In crystals atoms 
have an orderly arrangement, yet no difference has been found 
in the weight of any crystal when it is set on end or laid on its 
side. This fact, along ’with the complete independence of elec- 
tric conditions, show that gravitation is neither an electric nor 
a magnetic phenomenon. 
The ether, so far as our knowledge goes, is a homogeneous 
isotropic continuum. In the conveyance of light and of elec- 
tric strain it shows the properties of an elastic solid. To plane- 
tary motions and to ordinary motions on the earth it offers no 
appreciable resistance, and may therefore be called a fluid. 
Michelson and Morley have shown that the ether close to and 
in the earth moves with the earth, which indicates that the 
ether does not move among atoms without some resistance cor- 
responding to friction. The existence of an ether strain such 
as that in a ley den jar also shows that there is a resistance on 
the part of the ether to the kind of motion that takes place in 
the electric discharge. Ether has mass, since it conveys energy 
by waves which have a finite velocity. Lord Kelvin has pointed 
out that the apparently inconsistent properties of the fluid- solid 
ether are analogous with the properties of ordinary matter. 
Pitch or taffy, either of which can be bent or moulded easily 
by a steady pressure, is shattered like glass by a quick blow 
from a hammer. The ether in like manner yields easily before 
