Figs. 5 and 6, by which a current is sent round the electro-magnet, D
(Fig. 1), attracting the armature, and drawing the disk forward
sufficiently for the roller at I to pass over the center of one of the
pins, and so drop in between that and the next pin, thus completing the
motion, and holding the disk steadily opposite the figure. This action
takes place on any meter completing a unit of measurement of (say) 1,000
cubic feet, at which point the contact makers touch. But suppose one
meter should be moving very slowly, and so retaining contact for some
time, while other meters were working rapidly; the armature at D would
then be held up to the magnet by the prolonged contact maintained by the
slow moving meter, and so prevent the quick working meters from
actuating it; and they would therefore pass the contact points without
recording. A meter might also stop dead at the point of contact on
shutting off the air, and so hold up the armature; thus preventing
others from acting. To obviate this, we apply the disengaging apparatus
shown at L (Fig. 4). The contact maker works on the center, m, having an
armature on its opposite end. On contact being made, at the same time
that the magnet, D, is operated, the one at L is also operated,
attracting the armature, and throwing over the end of the contact maker,
l¹, on to the non-conducting side of the pin on the disk. Thus the whole
movement is rendered practically instantaneous, and the magnet at D is
set at liberty for the next operation. A resistance can be interposed at
L, if necessary, to regulate the period of the operation. The whole of
the meters work the common dial shown in Fig. 1, on which the gross
results only are recorded; and this is all we want to know in this way.
The action is so rapid, owing to the use of the magnetic disengaging
gear, that the chances of two or more meters making contact at the same
moment are rendered extremely small. Should such a thing happen, it
would not matter, as it is only approximate results that we require in
this case; and the error, if any, would add to the apparent amount of