01 . 
L. Schwendler— On Eleetric Light Measurements. [March, 
C = 0-33 
yW 1 — w 1 
J m + r 
therefore the observed current never can be higher than this value, and 
this fact gives a criterion for trustworthy observation. 
General Specifications of an Electric Lamp required 
for use in India (East Indian Railway). 
The lamp to be constructed on the Serrin principle , with the following 
alterations :— 
1. All parts of the lamp, including clockwork, &c., &c., to he made 
of gun-metal. No steel or iron is to be used except in the electro-magnet 
and its armature. 
Even the axles of the wheels and the fly-escapement must be made of 
gun-metal. 
2. The carbons to be used in this lamp may be of any shape—round, 
triangular, or square. The carbon-holders should be sufficiently large to 
hold a round carbon of 18 mm. diameter; and should be constructed in 
such a manner that they can hold carbons of a much smaller diameter, 
and also that by the expansion due to heating, the carbons should not 
become loose in their clamps. 
The construction of the carbon-holders in the Siemens lamp appears 
to be good, and should be adopted in this lamp. 
With 18 mm. carbons the lamp should bum 8 hours. 
3. The screw for regulating the tension of the spring or springs 
which act in opposition to the magnetism of the electro-magnet should 
move 1 mm. by one whole turn. 
In order to know the adjustment at any one time, and to be able to 
make the same adjustment again, a millimeter scale is to be attached, by 
which the movements of the screw can be read. The circumference of the 
head of the screw is to he divided into ten equal parts. Hence by this 
arrangement the comparative tensions of the spring or springs can be read 
up to 0T mm. 
This micrometer screw, after the lamp has been regulated for any 
given current varying within two known limits, is to be fixed by a clamp 
and screw to keep that adjustment constant. 
4. The distance between the electro-magnet and its armature is 
also to be made adjustable by a micrometer screw, provided again with 
millimeter scale like the above, and with a clamp and screw, for makino- 
any best adjustment constant. 
