Intelligence and Miscellaneous Articles. 337 



to the further progress of an important application of the resources 

 of nature. 



It will be seen from the foregoing that I have called the light- 

 intensity 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 posi- 

 tion 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 illuminating-purposes, and may 

 be 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, be- 

 cause the electrodes have a volume, and moreover the positive elec- 

 trode is hollowed-out like a dome, and it is the highest point of that 

 dome which contains the most intense light, which is mostly lost. 

 How much this loss in each case will be, depends on a variety of cir- 

 cumstances. 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 two 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 mm., then the sum of 

 the lengths of two arcs will not be 3 mm. 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 for 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 elec- 

 tric 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 : — 



The consumption of power per unit of measured or external light 

 is a function increasing with the number of lights produced by a 

 given current in a single circuit — supposing, of course, always that 

 the sum of resistances of the n arcs is equal to the resistance of 



