84 
L. Schwendler— On 'Electric Light Measurements. [March, 
■will invariably do an enormous amount of barm towards the further pro¬ 
gress of an important application of the resources of nature. 
It will he seen from the foregoing that I have called the light inten¬ 
sity— measured intensity. For if we produce a light by any source, it 
will be at once perceived that not all the light produced by that source 
can be made available for illuminating purposes. A part of the total light 
will be lost for the special purpose of illumination, inasmuch as only 
a part of the total light is in a position to act on the Photometer, or 
which is the same, on the retina. Hence we may say, the total light 
produced by any means consists of two parts—the one is lost for illumina¬ 
ting purposes, and may he called internal light; the other acts on the 
retina, can be measured, and may be called external or measured light. 
For instance, of all the light produced in one electric arc, a considerable 
part is hidden by the electrodes between which the arc plays. Because the 
electrodes have a volume, and moreover the positive electrode is hollowed 
out like a dome, and it is the highest point of that dome, which con¬ 
tains the most intense light, which is mostly lost. How much this loss 
in each case will be, depends on a variety of circumstances. In the first 
place, all other conditions being the same, that loss will increase with the 
thickness of the electrodes. The loss of light -will further increase with a 
decrease of the length of the arc. By length of arc is to be understood 
the distance between the highest point of the hollow of the positive 
electrode and the apex of the negative electrode. Hence already in the 
case of one arc, although naturally we have here the longest arc, for the 
given current and the given electrodes, the light lost or the internal light 
may represent a considerable portion of the total light produced in the 
arc. 
If we produce tivo arcs, it will be seen at once that the sum of the 
losses must be greater than the loss in one arc. Hence the sum of the 
measured intensities of two lights must also be smaller than the measured 
intensity of one light. Suppose the length of one arc, when a given 
current passes, is 3 m.m., then the 'sum of the lengths of tivo arcs will not 
be 3 m.m., but much less, in order to have the same current passing 
through the two arcs as passed before through one. From this it follows 
that the loss of light must increase rapidly with the number of lights, and 
moreover that soon a limit to the possible practical division of the electric 
light is reached, leaving out the question of economy altogether. 
This constitutes one of the reasons why the division of the electric 
light becomes less and less economical with increase of the number of 
lights, and that soon a practical limit will be reached for the division. 
To express this result more definitely, we may say: 
