100 Proceedings of Royal Society of Edinburgh. [sess. 
right. Is it not akin to inconsistency to say in effect — “ It is 
justifiable to violate, for convenience, the custom of writing an 
operator to the immediate left of the symbol affected, and to indi- 
cate the connection by some other method, but the justification 
only covers a limited violation of the custom. It matters not that 
the new method of indication will equally well serve whatever be 
the relative positions in a term of the operator and the symbol 
affected — we will strictly adhere to one part of the restriction 
hitherto imposed upon this relativity of position, though freeing 
ourselves from the other.” 
It may be — has been — urged that to place a V to the right of the 
symbol affected is as criminally ridiculous as to write X— for 
dx 
• It may be equally well urged that the removal of V to the left 
dx 
from its primitive position is on a par with writing — XY for 
dx 
x dY 
X dx 
It must be conceded that both of these violations of custom are 
objectionable, and cannot be justified, unless some convenience 
accrues greater than the counterbalancing inconvenience of having 
to show by some method, other than that of juxtaposition, the con- 
nection between the operator and the symbol affected. Whether 
such convenience does exist must be left undecided till we come to 
the applications. What I want to point out here is, that it is 
extremely inconvenient, and there is absolutely no ground whatever 
for not utilising this new’ method of indication in all cases where it 
is applicable. 
To take an instance. In considering Maxwell’s electrostatic 
theory below, we are led to consider the very simple stress, whose 
corresponding linear vector function <f> is given by the equation 
</>o) = V2)o>(5 , 
where £) and (& are the electric displacement and electro-motive force 
respectively.* The force per unit volume due to this is 
d<f>i d_& d<j>k dV^jiS dV^m 
dx dy dz dx dy dz 
* Maxwell’s Elect, and Mag., 2nd ed., § 68. 
