106 L. Schwendler— On Electric Light Measurements. [Mabch, 
The consumption of the carbon points is clue more to combustion than 
to disintegration. 
The incandescent part of the carbon points has so much more intensity 
of light than the flame that the latter causes a shadow. 
The hissing noise produced by the electric arc is, I believe, clue to 
the formation of a vacuum round the incandescent carbon points. 
The noise is much stronger in a short than in a long arc. It may 
also be due in part to the disintegration of the carbon points. The noise 
of the electric light in a quiet room is simply unbearable. This speaks 
only against the use of the electric light for domestic purposes. 
There can be no doubt that one length of arc is best under given 
circumstances, considering both the intensity and regularity of the light. 
The light permanently decreases with length of arc, hence the arc 
should be made as short as possible. This would, however, be bad for the 
constancy of the light, and may also spoil the dynamo-electric machine. 
Hence adjust the commutator by turning the brushes in the direction of 
the rotation until only small sparks are observed. 
If this is impossible make the arc longer by lessening the tension of 
the spring. 
In this manner the best length of arc can be exjjcrimentally found. 
This would give the best tension of the spring at the starting point. 
Now let the dynamo-electric machine run for several hours, and make 
the same experiments, when the best tension of the spring will be found 
somewhat less. Take the mean of the two tensions and fix the micrometer 
screw. 
Proportionality of light and current — 
Although the light produced in the arc must be very nearly propor¬ 
tional to the total energy consumed in the arc (minus the energy expended 
in giving the disintegrated carbon particles velocity), the resistance of the 
arc decreasing with increase of current, it follows that the light cannot be 
proportional to the square of the current. 
If we make the highly probable supposition that the resistance of an 
arc of constant length is inversely proportional to the current which passes 
through, then the light produced would be proportional to the current. 
This appears to be the case. 
The conduction of the arc appears to be due to two causes, rarefied 
air and carbon particles flying in both directions. 
Both causes would point towards an inverse proportionality between 
current and resistance of arc. 
There are many other novel points of great interest to be discussed, 
and many more practical and scientific results, I have no doubt could be 
