224 
THE TELEGRAPH. 
is fitted together, but when once this is done, these parts remain 
unchanged. 
The most suitable ink for the siphon is aniline blue, soluble 
in water. By dissolving in half a glass of water as much of 
the crystaline substance as will lie on the point of a penknife 
we obtain a perfectly fluid ink of a fine deep-blue colour. This 
ink is preferable to any other because it does not get thick or 
deposit any sediment, and as it can be prepared in small 
quantities it is very handy. 
Adjustment of the electrical mill .—This apparatus is at once 
an electro-magnetic engine, and an electro-static induction 
machine. By the former action it brings the paper under the 
siphon ; by the latter, it electrifies the ink which is projected 
in a continuous line. With a long cable and a fine siphon this 
last function is the more important; whilst with shorter, the 
arm of the lever need not be so long, and where a greater speed 
may be attained it is more particularly the former that is 
required. 
If the mill does not turn with sufficient rapidity, the contact 
piece x must be changed, so as to diminish the resistance of 
the circuit, and this will immediately increase the speed. The 
adjustments of the spring contact points should be very exact, 
and the little cups, in which the friction rollers that support 
the axle work, should be kept full of watchmaker’s oil. If, 
after all these precautions, the mill still turns slowly it will be 
necessary to increase the power of the battery that works it. 
Three of Sir W. Thomson’s large surface-cells described in 
a former chapter are sufficient for the purpose. 
The electro-magnetic contact interimptor consists of two 
platinum points, one of which is fixed, while the other is 
alternately raised and lowered by a steel spring moved by the 
segment of the divided wheel. It is easily seen if the 
platinum points are too far apart, and in that case the electro¬ 
magnet will not successively act on the accumulators as long as 
required, and the result will be a diminution of power ; on the 
other hand, if the contacts last too long, the electro-magnet 
will continue to act on the accumulators after they have passed 
its poles, and will tend thus to retard and stop their movement. 
The adjustment therefore of this spring is one of the most 
important points of the apparatus. This can readily be done 
