results. To obviate these a large storage battery was ordinarily introduced, connected across the mains adjacent to the main generator. This is so designed and arranged that when there is a rise of load the battery will discharge current to the work-circuit and thereby prevent the extra heavy load from falling upon the main generator. Where there is a lighter load in the work-circuit the battery charges, thereby taking up some of the force of the main generator. When the load on the work-circuit is of the average for which the system is adjusted the battery "floats," as it is termed, neither charging nor discharging. The storage battery is slow in operation, and to increase the rapidity of its discharge or charge, as the occasion required, there was introduced a dynamo with armature in series with the battery which compels the battery to perform its function rapidly. The booster voltage operates in either direction as the demand is for charge or discharge according to the changes of load in the workcircuit.

There is no expert testimony in the record and we have given such a description of the art as we have been able to gather from the decisions of the tribunals of the Office, and the argument of counsel.

The respective inventors in this controversy, whose devices, though specifically different, conform to the broad terms of the issue, sought to apply this principle of control in a system having an alternating current and a direct-current generator, in combination. They have conceived the idea of duplex control of a battery connected with the direct-current side of the system which will maintain the load on each generator steady, itself receiving or supplying current when the sum of the load of the two circuits is substantially below, or above, respectively, the average for which the combined systems are adjusted. As before said, the system of each inventor is within the broad terms of the issue, and it is, therefore, unnecessary to discuss the specific differences between them.

The issue calls for the following elements: 1. A combination of alternating and direct current circuits. 2. An appropriate converter. operatively connected between the two circuits. 3. A battery operatively arranged in respect to the direct current circuit. 4. Means adapted to cause the battery to charge and discharge, and operatively arranged to correspond to variations of load on either circuit. The controversy respecting the claim by Woodbridge of actual reduction to practice turns, chiefly, upon this requirement of means to cause the compensatory storage battery to charge and discharge in response to variations of load upon either circuit.

Winship is the senior party, having filed his application March 11, 1905. Woodbridge filed on April 19, 1905, and through failure in the Office to declare an interference, received a patent on May 8,

1906. Woodbridge's statement alleges conception of the invention in March, 1903; drawings about the same time; reduction to practice in October, 1903. Winship's statement alleged conception between July 22 and 26, 1904; sketches and disclosure about the same time; further disclosure in August, 1904, and again on December 14, 1904, in making a description, etc., for the purpose of applying for a patent. The only reduction to practice is that effected by filing the application.

Woodbridge had the burden of proof. To overcome Winship's prior application it was incumbent upon him to show a conception prior to Winship, and either actual reduction to practice, as alleged, or diligence in the prosecution of his invention at the time of Winship's entry in the field. The testimony taken by Woodbridge in chief contained no corroboration of his conception prior to the alleged reduction to practice in October, 1903. In the course of his testimony he offered in evidence a sketch of the specific form of his invention, saying that it was prepared for his patent application. This sketch is a printed blank of the patent department of the Electric Storage Battery Co., of which Woodbridge was chief engineer. At the bottom of the drawing and brief description in writing, appears a printed form of certificate with blanks for dates. With the blanks filled up it reads:

This idea was conceived by me Dec. 14, 1904, and the above drawing and description was made by me Jan. 5, 1905, and was shown and described to each of the undersigned witnesses at the date set opposite his name.

This bore the signature of Woodbridge and that of an attesting witness, A. McNichols, as of date January 5, 1905.

Winship's testimony as to conception on the earlier dates alleged by him was uncorroborated, but there is no doubt of the last date alleged, December 14, 1904, on which he disclosed the invention completely to his patent solicitor, for the purpose of applying for a patent. His earliest date of conception is, therefore, December 14, 1904, and for reduction to practice he stands on his filed application of March 11, 1905. Woodbridge then took what is entitled, rebuttal testimony, attempting to show that the sketch. No. 5, heretofore described, represented an earlier conception of the specific idea. To support this he read certain letters alleged to have passed between him and R. C. Hull, district engineer of the sales department of his company at Cleveland, Ohio; the first of the series being a letter of Hull dated October 27, 1904, to which the reply was under date of November 7, 1904. These letters were produced by Woodbridge. Hull was not examined, and there was no other evidence relating to their writing, despatch, and receipt. The tribunals of the Office rejected this evidence, upon objection, on the ground that it was not rebuttal evidence and ought to have been introduced in chief.

Each tribunal of the Patent Office held that while the experimentation of Woodbridge at Columbus, Ohio, in October, 1903, may have demonstrated the conception of the broad idea of the invention, it was not an actual reduction to practice. It was said by the Commissioner in conclusion:

Whether, therefore, the Columbus test be held to embody the invention in issue or not, Woodbridge cannot prevail. If it did not embody the invention, Woodbridge was later than Winship in both conception and reduction to practice. If it did, Woodbridge was the first to conceive, but the last to reduce to practice, and was not diligent in reducing the invention to practice at the time Winship entered the field.

This unanimity of decision necessarily imposes the burden upon Woodbridge to make out a clear case of error in the decision appealed from.

The first question to be considered is whether there was error in rejecting, or refusing to consider the evidence offered by Woodbridge in rebuttal. We think there was not. Orderly rules of procedure must be observed in the Patent Office as elsewhere. The junior party had notice of the dates claimed by his opponent. The proper order of his procedure was to introduce all of the proof upon which he relied to support his own allegations. This additional testimony ought then to have been introduced. It is not in rebuttal of the case made by Winship. Counsel for appellant claims that he was led to believe, upon the closing of Winship's case in which he only proved the date of December 14, 1904, that the latter took the position that the issue should be so narrowly construed as to exclude Woodbridge's Columbus disclosure. To meet this contention that it should be construed narrowly the additional evidence was introduced to show that he was first to conceive under this narrow construction. Further, also, that as Winship confined his corroborating evidence of conception to December 14, 1904, and thereby abandoned his earlier date, alleged as of July 22, 1904, which antedated the Hull letters, it was proper to show that the idea illustrated by sketch No. 5 as of December 19, 1904, had been earlier conceived and then communicated to Hull early in November, 1904. As Woodbridge was bound to introduce his evidence first, he had his own statement and that of Winship (which may be called the pleadings) by which to determine the extent to which he should go in proving his case in chief. He could not be misled by evidence which his opponent had not then introduced, or by a position respecting the scope of the invention which he had not then indicated in any manner. Having rested his case in chief, he is limited to rebuttal testimony after the closing of his adversary's proof. Realizing his inadvertency, he might possibly have obtained leave to reopen his case-in-chief to cure the effect of it. However this might be, he took no such step, and must abide the consequences.

Under our view of the evidence relating to reduction to practice by Woodbridge at Columbus in October, 1903, we may assume that he then had in mind an invention that is within the terms of the issue, and treat him as the first to conceive.

It appears that this test was made October 14 and 15, 1903, in connection with the power plant of a street-railway company at Columbus, Ohio, by J. L. Woodbridge, the inventor, and J. E. Woodbridge, an engineer of the General Electric Co., at Schenectady, N. Y., who had installed the entire plant of the railway company. Both witnesses testified as to what occurred, after a lapse of five years. J. E. Woodbridge made a written report of the operations at Columbus to his own company, under date of October 22, 1903, which was read in evidence. This states tests 1, 2, 3, 4 and 5 as made. Test No. 1 is the only one of these which Woodbridge claims could have embraced the invention which it is claimed was then reduced to practice. This report was submitted to J. L. Woodbridge, who made no comment upon it, but gave it his general approval. J. E. Woodbridge was not informed of any special purpose that J. L. Woodbridge had in view. J. L. Woodbridge was asked in cross-examination, to point out any language in the report which suggested that they were trying to see how much they could cause the battery to act to assist the fluctuations originating outside substation E (where the tests were made.) To this he answered as follows:

I do not know that there is any language in this report which attempts to indicate what I was trying to demonstrate. Mr. J. E. Woodbridge joined me in these tests with an avowed purpose quite different from mine. He was looking for combinations which could insure the greatest stability of operation with respect to the direct-current output of the rotary, and was therefore looking to produce results exactly the opposite of those which I intended to produce. This is obvious from the language under the heading "General conclusions." In this paragraph he states that for small plants the differential booster is to be preferred. The differential booster is designed to prevent, as far as possible, the battery from charging and discharging in response to any changes on the alternating-current circuit, but is designed to maintain a constant directcurrent output from the rotary converters. Mr. J. E. Woodbridge was endeavoring to ascertain what combination of apparatus would most nearly secure this result. His report to his own company therefore includes his observations and conclusions on that point.

It does not appear from J. E. Woodbridge's testimony that the tests were made with a view to ascertain anything else than he, himself, had in view. In his report he states that test 5 was preferable to test 1, and recommended 2 and 5 in preference to others. The Examiners-in-Chief say that further uncertainty in this test, in so far as the present invention is involved, is found in the conditions prevailing in the system at the time. It appears, they say, that the railway was supplied by an alternating-current generator, situated sixty miles away, which gave a high-tension current that was stepped

down at a number of intermediate substations by stationary transformers and fed to rotary conductors. At the Columbus station there were two shunt rotary converters supplemented by engine-driven direct-current generators, also in parallel with the rotary converters across the direct-current bus-bar. The direct-current generators, however, were disconnected during the conduct of experiment No. 1. They further say:

A battery and booster in series were also connected across the direct-current bus-bar, the field of the latter being compound wound, one coil in series with the battery and the other in shunt and capable of manual control. As we understand it, this arrangement of battery and booster is a common one when a battery is employed to correct the irregularities of the load of a direct-current system. It is also well known, and appears from the testimony of Woodbridge, that the function of the booster so connected is to magnify the charge and discharge of the battery caused by fluctuations in the voltage across its terminals. The booster does not initiate or determine the charge or discharge. That would take place as surely and at the same time if no booster were present, but would merely be less in amount.

In this connection, they quote from an article of J. L. Woodbridge, published in Cassier's Magazine for November, 1905, in which he says:

The simplest type is that with the booster field-coll in the battery-circuit. This is commonly called the "straight-compound" booster. In this type of installation, the booster alone cannot cause the battery to charge and discharge, since it depends upon the current in the battery-circuit to actuate it. It is necessary, therefore, to provide some outside cause to produce battery discharge or charge and the booster will then become a factor in determining the amount of such charge or discharge. As already mentioned, the only way to cause the battery to discharge is to lower its terminal voltage.

We shall not pursue the suggestions made as to the state of the alternating-current generator, sixty miles away, and the unnoted fluctuations of that current through causes operating there and on the line elsewhere, for we must confess our inability to appreciate what effect these may have had. It is, as before remarked, an essential feature of the issue that the means shall be adapted to cause the battery to charge and discharge, and operatively arranged to respond to variations on either circuit, that is the alternating and the direct circuit. This is distinguishable from means adapted merely to augment or magnify the charge and discharge of the battery. There must be a regulating apparatus that shall be acted upon by a change in the load of either of the circuits, whether there is a change in the other or not.

Now while J. L. Woodbridge testifies that in the Columbus test the battery charged and discharged in response to variations of load of either the direct-current or the alternating-current circuit, he is not. corroborated in this by J. E. Woodbridge. The latter says the battery