the circuit is complete between the earth and any one of these branches a current of electricity will pass through the thin leaf of metal, rendering it incandescent, and so produce light." The system of measurement was next described; and the specification continued:-"The electromotive force of the electric conducting mains should be kept as nearly as possible constant, at, say, 100 volts or B.A. units of E.M.F. A number of Plante's (lead and sulphuric acid) cells joined together in series between the main and the earth will serve as a kind of reservoir for electricity." The conductors are next described, then :-" In order to keep the E.M.F. in the mains constant, it is desirable to have in the first place several generating machines; next, it is necessary to have some regulator, such as that about to be described." The regulator consisted of a quadrant electrometer connected with the main and earth "in the usual way." The needle, on coming into contact with fixed pegs, would complete local circuits, and so actuate levers acting on valves, thereby increasing or diminishing the supply of steam to the generating engines.

The complete specification1 was for "improvements in [obtaining light by electricity, and in conveying], distributing, [measuring], and regulating the electric current for [the same], obtaining light by electricity and in the means or apparatus employed therein." The lamp was first described, consisting of a platinum or platinum alloy wire or leaf. Then came the general system of distribution as mentioned in the provisional and illustrated by Fig. 3, A being the generator, and the conductors being shown by the lines, terminating in lamps, from which the "earth" wires (not shown) led to "earth." The mode of connecting them to gas or water pipes was described. The measuring apparatus (a shunted voltameter) was also described. "The E.M.F. of the electric conducting mains should be kept as nearly as possible constant, say at 100 volts or B.A. units of E.M.F. A number of secondary batteries, such as Plante's (lead and sulphuric acid), such batteries being joined together in series between the main and the earth, will serve as a kind of reservoir for the electricity. The cells should have a very large conducting surface, and there should be several batteries connected up at various points of the mains, so that by increasing the E.M.F. during the hours when not much electricity is being used, they will become charged and the electric force will be stowed up in them, so that a sufficient supply will be available when the E.M.F. falls, owing to the draft from the mains when the force is most used and needed. The number of cells in each of these batteries will depend on the E.M.F. of the mains."

"Fig. 5 is a diagram representing a secondary battery joined up between the main and the earth for the purpose above described. E indicates earth, and / lamps.3. . . In order to keep the E.M.F. in the electric mains

1 Only those parts are inserted which are necessary to appreciate the decision. The amendments made by disclaimer are shown:-the words in square brackets were omitted, and those in italics inserted.

Figs. 3 and 5 are diagrammatic, and are here given.

3 A description of the conductors were here omitted by disclaimer.

constant, it is desirable to have in the first place several generating machines, also a number of reservoir batteries, as before explained; [next it is necessary to have some regulator such as that about to be described]."1 The quadrant regulator was disclaimed and its description struck out.

The claim in the amended specification was for "the employment as described of secondary batteries as reservoirs of electricity in combination with a mode or system of distribution such as is hereinbefore explained.”

In an action for infringement against the defendants the following facts, inter alia, were proved :

That Planté cells, when discharging, had a smaller potential difference between their terminal plates than when being charged, hence they could not act as automatic regulators of potential in the mains.

That they were useless unless used with a switch, so that the number of cells in the battery could be varied with the rise or fall in potential during charging and discharging. Without a switch the pressure necessary to charge the batteries would break down the lamps. This was illustrated by the curves here reproduced. From them it appears that if the battery

2.5

2.4

Curves by Prof. WE.Ayrton FR.S.

-Time of Charging in Hours - -

--Time of Discharging in Hours---→

1 2 3 4 5 6 7 8 9 10 11 12 13 14 14 1 2 3 4 5 6 7 8 9 10 11 12 13 14 143

(say of 50 cells) be arranged to discharge at 100 volts, it must be charged at a pressure from 105 to 115 volts, which the lamps would not bear.

But if that difficulty were overcome, it was proved that there would be considerable irregularity both in pressure and current during the discharge, so that the battery could not act as a regulator. The amount of this irregularity is shown by Prof. Kennedy's diagram given below.

That Planté cells were well known in 1878, and had been used for storage

1 These words were struck out by disclaimer.

2 In this diagram produced at the trial the descending curve was continued further. It was originally published by Prof. Ayrton and Messrs. Lamb and Smith to illustrate their paper on The Chemistry of Secondary Cells." The breaks at B, C, and C' were due to the stoppages in an experiment to remove certain test plugs. The change of potential of the battery in action is according to the continuous curve. See Vol. XIX. p. 660 of The Journal of the Institution of Electrical Engineers.

in connection with arc lighting, but not in connection with dynamos for incandescent lighting.

That in 1878 no successful incandescent lamp had been invented. Nor was it known that in large districts the earth could not be used as a return conductor-the term "earth was technically used for return conductors.

(130

སྐྱེ

Diagram 1 by A. KENNEDY F.R.S.

Showing irregularity of Potential & Current from a Battery of
60 31 Pl. cells discharging with variable external Resistance
Potential at end of Previous Charge -154.8 or 2.58 per cell.

108.3

103.6

96.3

Volts per 50 cells

Current in AMPÈRES

60

L40

80

The patent was held invalid at the trial on the grounds of disconformity and insufficiency, and the opinion expressed that otherwise it was new, was subject-matter, and had been infringed (9 R. P. C. 221).

Both parties appealed.

Held, by the Court of Appeal

That without further invention or experiment as regards "switching" the invention was useless for the purposes described by the patentee.

That the specification was insufficient, owing to the want of such directions as would enable a constant pressure to be maintained in the mains.1 The patent was therefore invalid.

That the invention claimed in the amended specification (regulation by batteries) was different from that described in the provisional (storage by batteries and regulation by regulator).

2

This follows from the preceding finding. It is looking at the same matter from a different point of view.

2 This finding (at p. 419) was not enunciated until the patent had been declared invalid. In coming to the conclusion that the amended complete specification was disconform to the provisional, the learned Lords Justices followed the decision of the Court of Appeal in Gaulard & Gibbs' Patent (6 R. P. C. 215), in which case there was a strong analogy as to the facts, without noticing that the House of Lords did not approve of the

Per Lindley, L.J. (p. 416): "An invention is not the same thing as a discovery. When Volta discovered the effect of an electric current from the battery on a frog's leg, he made a great discovery, but not a patentable invention. Again, a man who discovers that a known machine can produce effects which no one knew could be produced by it before, may make a great and useful discovery; but if he does no more, his discovery is not a patentable invention:-Britain v. Hirsch, 5 R. P. C. 232; Harwood v. G. N. Ry. Co., 11 H. L. C. 654; Horton v. Mabon, 12 C. B. N. S. 437 ; Saxby v. Gloucester Wagon Co., 7 Q. B. D. 305. He has added nothing but knowledge to what previously existed. A patentee must do something more: he must make some addition, not only to knowledge, but to previously known inventions, and must so use his knowledge and ingenuity as to produce either a new and useful thing or result, or a new and useful method of producing an old thing or result. On the one hand the discovery that a known thing-such, for example, as a Planté battery-can be employed for a useful purpose for which it has never been used before is not alone a patentable invention; but, on the other hand, the discovery how to use a thing for such a purpose will be a patentable invention if there is novelty in the mode of using it, as distinguished from novelty of purpose, or if any new modification of the thing, or any new appliance is necessary for using it for its new purpose, and if such mode of user, or modification, or appliance involves any appreciable merit. It is often extremely difficult to draw the line between patentable inventions and non-patentable discoveries, but I have endeavoured to state the distinction as I understand it, and so far as is necessary for the purposes of the present case. I have, of course, been guided by the previous decisions on the subject, and especially by Harwood v. G. N. Ry. Co., which is the most instructive of them all."

1

At p. 417: ". . . The utility of the alleged invention depends not on whether by following the directions in the complete specification all the results now necessary for commercial success can be obtained, but on whether by such directions the effects which the patentee professed to produce could be produced, and on the practical utility of these effects. Can it be said that the invention as described in the amended specification was, in 1878, a practically useful addition to the then stock of inventions? To judge of utility, the directions in the amended specification must be followed, and, if the result is that the object sought to be attained by the patentee can be attained, and is practically useful at the time when the patent is granted, the test of utility is satisfied. Utility is often a question of degree, and always has reference to some object. 'Useful for what?' is a question which must be always asked, and the answer must be, useful for the purposes indicated by the patentee."

finding of disconformity by the Court of Appeal in that case (ante, p. 64). An inventor should not rely too much on this being an example of disconformity.

1 As re-stated by Lindley, L.J., in Moser v. Marsden, 10 R. P. C. 358, and followed by Smith, L.J. (ibid., p. 363). Followed in Pirrie v. York St., &c., 11 R. P. C. 438, 453, 455 ; Thierry v. Riekmann, 12 R. P. C. 427; and Acetylene Ill. Co., Ltd. v. United Alkali Co.,

20 R. P. C. 173.