844 The Philippine Journal of Science 1921 
If an umpire were required to measure a baseball, he would 
hardly attempt the feat while the ball was speeding toward him 
from the pitcher’s hand. He would first get it in his hand, at 
rest, as far as he is concerned, and then measure it. A scientist 
has an advantage over the umpire, in that he can measure 
the properties of things which are in motion relative to him; 
but if he does so, and if they are moving very fast, he must 
apply a correction to his results which is known as the Lorentz 
transformation. _ 
Now if a scientist wishes to define his units in an absolute 
manner he naturally measures something which is at rest 
relative to him, so that he can be sure of his results. 
There are certain quantities which involve motion, and are 
therefore inconsistent with relative rest, but he has a wide 
range for the practical constancy of these quantities, which 
becomes a theoretical constancy in the limiting case. The 
conditions for the measurement of the velocity of light do not 
bother him, because our premise states that this value, if 
measured in his vicinity, is apparently a constant. He must 
still be cautious, however, and measure only light in his 
immediate vicinity. If he tries to measure the velocity of 
light on some body that is moving relative to him he still 
must correct his measurements. 
The relativists claim that a unit of length, time, or mass 
is meaningless except for a “frame having a certain velocity.” 
Does that mean that my measurement of the density of water 
to-day is meaningless to-morrow when my “frame of reference” 
is different? ‘Oh, no,” they say, “the numerical value of the 
measurement will still be good, but both the density and the 
size of your units will have changed without your knowledge. 
You cannot compare to-day’s units or to-day’s actual density 
with to-morrow’s units or to-morrow’s actual density without 
a knowledge of your velocity to-day relative to your velocity 
to-morrow.” 
This statement is fallacious. There are many ways in which . 
we can define our units of length, time, and mass, in terms of 
absolute units which are not affected by the velocity of 
“frame.” Without saying anything about the absolute mass 
of an electron, we have given, from the Relativity Principle 
itself, that the apparent mass of an electron, properly meas- 
ured, is a constant not affected by change of “frame.” We 
have given the same as to the apparent charge of an electron 
and the apparent velocity of light. 
