95 
1879.] L. Schwendler —On Electric Light Measurements. 
5. The clockwork and all regulating parts of the lamp to be entirely 
covered by a strong metal case, which is to be constructed in such a 
manner that it can be taken off or put on without interfering in any way 
with the adjustment of the lamp. The best, I think, would be to make 
that case cylindrical, opening like a door in two halves on hinges, and with 
a key for closing it. There is no limit to the actual size of the case, since 
the lamp is intended for lighting up by the method of “ diffusion” with an 
opaque reflector, which is placed and begins alove the cover. 
None of the adjustable parts of the lamp are to protrude, as it is 
intended not to touch the lamp after its proper adjustment, which is done 
in the laboratory only. 
It is quite a mistake to give people easy regulating means. That 
will never answer in practice. People, as a rule, will turn anything in the 
opposite direction they ought to do; then they get excited, and the failure 
is attributed to the lamp instead of to the people. 
Each lamp has only one best adjustment for any given current varying 
between two known limits, and the best adjustment is made constant by 
fixing everything. The case or cover is then closed, and. the lamp put up 
for use. 
6. The electro-magnet which pulls the arc should offer no more 
resistance than 0 - 02 S.U. It is to be shunted by another Electro-Magnet 
which offers exactly the same resistance (002 S.U.) 
Hence, one half of the current passes through the electro-magnet of 
the lamp, and is made use of for pulling the arc. The amount of iron 
used in the electro-magnet, and the number of convolutions should be 
such, that at the mean distance of the electro-magnet from its armature, 
the magnetic force is strong enough to produce an arc of 2 5 mm. against 
the mean tension of the spring or springs when employing a current of 
about 25 Webers. 
The magnetic action of the shunt for the same current should be 
about double that of the electro-magnet of the lamp, in order to leave 
a margin for a finer adjustment, i. e., equalization of the magnetic action 
of the two. 
In the foregoing it has been supposed that the shunt does not act on 
the armature. But it can be easily conceived that the free magnetism of 
that shunt may be made to assist the electro-magnet for regulating the 
I consider it, however, better not to do this, especially when the 
currents produced are sufficiently strong, above 30 Webers, which will be 
the case when using a dynamo-electric machine, as described in the first 
part of this Appendix. 
