82 Dr. E. Obach on an Improved Construction 
shunt are subjected, do not of course in the least disturb the 
ratio of their resistance, since they both consist of the very 
same alloy. 
As the current only passes round the needle once and, if 
powerful enough, produces deflections even if the ring is 
almost horizontal, it is hardly necessary to call attention to 
the fact that the wires leading the current to the instrument 
should be so arranged that they cannot act upon the needle; 
still I have seen instances where this simple and almost self- 
evident precaution has been strangely neglected. I thought 
it therefore best to have special leading wires provided which 
are absolutely inactive upon the needle, and may therefore be 
named " adynamic leads." These leads consist of a number 
of well-insulated copper wires stranded together in a peculiar 
manner, and covered with a cotton braiding, similar to the 
ordinary speaking-tubes. The cable thus formed is quite 
flexible, and without the slightest action upon a magnetic 
needle. I sent a strong current through several turns of such 
a cable, and held it close to a delicately suspended magnetic 
needle, but could not detect any effect whatever upon it. 
One half of the wires is covered with a differently coloured 
material to the other half ; and the wires of each colour are 
united at both ends of the cable, and there soldered to a stout 
piece of copper wire. The adynamic cable can be made in 
any length and for different current-strengths; and as it offers 
only a small resistance, it can be employed to convey the 
current to be measured to a locality where the needles are not 
disturbed by machines or wires. 
The Adjusting Parts and the Compensating Magnet. 
"With regard to the adjustment of the instrument, it suffices 
to say that, besides the necessary le veiling-arrangements, it is 
provided with clamp-rings for tightly holding the pillar as 
well as the movable coil without interfering with previous 
adjustments, and in the same manner as is often done with 
mathematical apparatus. The final adjustment of the axis of 
the coil into the meridian is performed by means of a fine 
screw, which proves very useful for correcting, during a series 
of measurements, the occasional variations of the zero position. 
As long as the galvanometer stands in the same position, 
the " constant" as a rule, changes but little even from day to 
day. If, however, the instrument is taken from one place to 
another, great changes in that respect will occur, amounting 
sometimes to many per cents. These changes do not of course 
interfere with the accuracy of the measurements, because the 
" constant " can easily be redetermined with a known EiM.F. 
