The following drawing, similar to the third figure of the patent, illustrates the apparatus and circuits described in the specifications:

The different parts of the apparatus illustrated and its operation are thus described in the specifications:

"D, D, D, D, represent separate latent signal instruments constructed as I have described, one being placed in each guest's room. Each instrument is connected by a separate wire with the receiving station or clerk's office, and each circuit leads through a separate spring-jack, M, and an annunciator, N, after which the circuits join and lead through a battery, R, to the ground. In a separate circuit are placed a battery, S, opposite in polarity to the battery R, and a sounder, T. This circuit terminates at one end in the ground and at the other in plug, t, one side of which is insulated, as shown. The apparatus is

represented as in its former condition, and all the separate circuits are open at the guest's instruments, a notch in each break-wheel being under the contact-springs.

"When any guest sets his instrument, it closes the circuit and drops the annunciator drop corresponding to that instrument and room, thereby making the clerk aware that that instrument has been set. It is to be observed that the instrument remains locked when set, for the reason that the polarity of the current in circuit is such as to repel the armature and make it lock the escapement. The circuit is thus closed at the room and remains so closed until the clerk opens it again by his action in releasing the latent signal. The annunciator may be provided with a continuous ringing arrangement to call attention, but in any case will prevent the drop from being raised inadvertently before the number is noted, as if so restored it will drop back again until the current is again opened at the room by proper means. The clerk thereupon inserts the plug, t, in the proper spring-jack, and the battery S, being of opposite polarity to the battery R, causes the guest's instrument to be released and transmit its signal, which is received by the clerk on the receiving instrument, T, for which purpose a sounder or bell may be employed to sound or a visual indicator or a register to record the signals received."

The claims of the patent in issue are Nos. 11, 12, 13, 19, and 20. Claim 19 is selected by the complainants as typical, and is as follows: "At each of several substations a calling apparatus including a circuit terminal and a manually operated element co-operating therewith and constructed to have with respect to the terminal a normal position of rest and one of action separate lines from these stations to a central station having a separate annunciator device for each such substation, and a common connection to a common source of current arranged to be controlled by the change of position of the substation manual element to begin the actuation of the corresponding annunciator device and nominally to continue this actuation until the said substation element is again in its position of rest, a switching connection at the central station for each such line arranged during its operation to interrupt the operation of the annunciator element; and co-operating therewith, a plug and cord adapted to be used in turn with all the switching connections, and a second connection controlled by the plug and supplying current of another character or condition; together with a magnetically controlled device at each substation arranged and adjusted to be controllable by the current controlled by the plug and not by the normal current and to operate as a notification to the transmitting operator."

The scope of this claim can best be appreciated by analyzing it and examining its elements in reference to the structure illustrated in the drawing and described in the specifications:

The first element of the claim is:

"At each of several substations a calling apparatus, including a terminal and a manually operated element co-operating therewith, and constructed to have with respect to the terminal a normal position of rest and one of action."

In the apparatus described and shown in the patent the substation is the latent signal instrument in the guest's room. The circuit terminal is the contact-spring, and the manually operated element is the break-wheel. These are nominally separated and in a position of rest; the spring being opposite a notch in the periphery of the wheel. They can be brought into a position of contact and, consequently, of action by rotating the wheel by hand.

The second element of the claim is:

"Separate lines from these stations to a central station having a separate annunciator or device for each such substation, and a common connection to a common source of current arranged to be controlled by the change of position

of the substation manual element to begin the actuation of the corresponding annunciator device, and nominally to continue this actuation until the said substation element is again in its position of rest."

In the structure described and shown in the patent, the parts embraced in this element are the separate signal circuits to each latent signal instrument, the individual annunciators, and the common battery.

The third element of the claim is:

"A switching connection at the central station for each such line arranged during its operation to interrupt the operation of the annunciator element."

In the apparatus described in the patent this element is the plug and cord at the central office. It is not regarded as of importance, however, that the annunciator should be cut out of circuit when the plug is inserted, for the patent says:

"Of course there is no objection in having the annunciator drop magnet left in circuit other than that it increases the resistance of the circuit."

The fourth element of the claim is:

"And co-operating therewith a plug and cord adapted to be used in turn with all the switching connections and a second connection controlled by the plug and supplying current of another character or condition."

In the apparatus described and shown in the patent, the plug at the central station is adapted to be used with all the switching connections and also controls a second connection with the battery S which is a different source of current from the battery R and of opposite polarity. When the plug is inserted in the spring-jack at the central station, the current flows from the second source of supply to the substation and energizes the magnet shown at the top of the left-hand figure so that it attracts its armature and releases the signaling instrument, which thereupon transmits its message to the central station. The last element of the claim is:

"Together with a magnetically controlled device at each substation arranged and adjusted to be controllable by the current controlled by the plug and not by the normal current and to operate at a notification to the transmitting operator."

In the apparatus of the patent this magnetically controlled device is, strictly speaking, the armature of the magnet above referred to. Speaking more broadly it is the magnet, the armature, and the breakwheel. They serve to hold the signaling instrument in its set position. and to release it so that the message can be sent in when the central office is ready to receive it. When the instrument is released its running down indicates either audibly or visually to the person at the substation that his message has been received.

And here it should be observed that all that the patent from beginning to end says about signaling from central to substation-the "outward call"-is as follows:

(1) The claim-as already noted-speaks of the "notification to the transmitting operator" and implies a prior transmitting operation on his part.

176 F.-23

(2) The specifications say:

(a) "This opening of the circuit (by the clerk), moreover, is so arranged as to serve as a return-signal to the guest and to indicate to him that his call has been noted."

(b) "When the clerk releases any latent-signal instrument, the guest is informed of the fact by observing the hand of the instrument or by the noise of the clock work in unwinding and is thereby assured that his wants are being attended to."

It is obvious from the claims and specifications as a whole that what the patentee especially desired to provide was means of communication from guest to central office, and not from central office to guestthat the outward notification was merely an incident to the inward call. Up to this point we have examined the claim in question in connection with the specifications and drawings, both of which refer to latent signal instruments. The whole organization of the patent seems to center around these instruments. There is much ground for contending that it cannot be read away from them-that the patent covers circuit connections only in connection with such instruments. And, if this be true, want of infringement is obvious, for it is conceded that the defendant does not employ latent signal instruments or any devices having similar functions.

The complainants, however, as already indicated, urge that the claim is for circuit connections, and not for the latent signal instrument or connections solely therewith, and the feature of the invention is said to be the "to and fro calling system" and the capacity for bidirectional calling embodied in the last element of the claim which we have examined.

Assuming then that we may eliminate from the patent, as the complainants have sought to do, all reference to the latent-signal instrument, it must still be clearly borne in mind that the "notification to the transmitting operator" of the last element of the claim is in the nature. of an acknowledgment signal rather than an independent signal. Indeed, it is not contended by the complainants that in the specific structure of the patent an initial message can be sent from the central office to the substation. And while, for the purposes of this case, we may assume that the specifications and drawings can be considered as applying (1) to a calling system and (2) to a latent signal system and confine ourselves to the former, we see no ground whatsoever for holding that the calling structure covered by the claim has any greater capacity for bidirectional signaling than that illustrated in the drawings of the complainants' own brief, viz., a capacity to send a signal from central to substation as the result of initial action there. To give the claim a broader application would be to depart from its own language as well as to wholly ignore the extracts from the specifications which we have quoted. We cannot accede to the proposition that the patentee can, under any doctrine of equivalents, change or add to the circuit connections of the patent so as to make the apparatus work in a different way or under different conditions.

Consequently, even if we admit that the claim is essentially for circuit connections and not for a latent signal instrument, still in view of its own language and of the specifications and drawings it must be

construed as covering only apparatus the parts of which act in such relation and subordination to each other that a signal from central office to substation follows only as the result of prior action taken at the substation. There must be an electrical or mechanical connection between the element used by the transmitting operator and the element employed for the return signal.

This limitation upon the scope of the claim renders it possible to confine the examination of the question of infringement within comparatively narrow bounds, and, possibly, to avoid altogether the question of validity. We have to look in the defendant's structure for the elements which we have found in the claim co-ordinated in the same way. If we do not so find them, infringement is not established, and it is unnecessary to consider the questions whether the patent is valid in view of the prior art, or whether on account of such art the patent should be construed broadly or narrowly. Only in case infringement is established is the question of validity important. Only in case the defendant infringes the claim as we have construed it is it important to consider whether we are justified in assuming, in accordance with the complainants' contention, that, the claim should be treated as covering circuit connections separate and apart from the latent signal instru

ment.

Turning now to the defendant's structure, we find that it is operating a telephone system consisting of: (1) The apparatus at each subscriber's station (the substation); (2) the lines connecting each subscriber's station with the central station or exchange: and (3) the apparatus at the central station for receiving and making calls and permitting the intercommunication of subscribers.

All the apparatus and circuits of the defendant's system are telephone apparatus and circuits, and there seems to be little ground for the complainants' attempt to differentiate between its signaling part and its telephone part. In order, however, to determine whether the claim in question covers any portion of the defendant's apparatus, we shall only examine those parts which the complainants assert constitute defendant's "signaling system" and have the limited capacity of bidirectional calling covered by the claim. We will attempt to read. the claim upon the defendant's apparatus.

At each subscriber's station in the defendant's system there is a break in the circuit at the telephone hook normally maintained open by the weight of the telephone receiver and closed when the receiver is removed from the hook and the latter moved by spring action into contact with the circuit terminals. Although the hook is actuated by a spring and not by hand, it may perhaps be regarded as the manually operated element of the claim. It is in a normal position of rest when the receiver is on the hook and is in a position of action when the receiver is off the hook and it is moved into contact with terminals. We will assume that this apparatus is covered by the first element of the claim, although, were we considering the prior art, it would be difficult to see why, in case this element appears in the defendant's structure, it does not also appear in the organization of the prior Cheever patent (No. 208,463). In that organization there is at a sub