International projectionist (Jan-Dec 1947)

Concentrated-Arc Light Sources Wfth Special Emphasis on the Literature of the Prior Art THE continuing avid interest of both the technical and lay press in the Western Union concentrated-arc (zirconium) lamp, as reflected by persistent efforts to invest it with properties which will shortly "revolutionize" lighting practices in both the production and exhibition of motion pictures, prompted a delving into the literature of the prior art in an effort to ascertain just what degree of "disclosure" is evidenced by this light source. Readers of I. P. will recall previous discussions of the W. U. lamp in these columns1' 2 in which were advanced cogent reasons why this unit is at present unsuitable for motion picture projection. That concentrated-arc light sources are by no means new is made clear by even a cursory inspection of the literature of the prior art. But even well-informed workers in the art might be surprised to encounter certain references dating back many years which, in terms of construction and operation, bear a striking similarity to the W. U. lamp. Early Significant References Of extreme significance are the references contained in the following U. S. patent issues: 1,152,675— Vreeland (Sept. 7, 1915) 1,154,514— Jacoby (Sept. 21, 1915) 1,178,542— Skaupy (April 11, 1916) 1,266,517— Meikle (May 14, 1918) 1,393.520— Friederich (Oct. 2, 1919) Nor is this all. But before considering even more persuasive evidence bearing on the "newness" of concentrated-arc light sources, some brief comment on the foregoing seems in order. Messrs. Vreeland, Jacoby, Skaupy and Meikle all disclosed, in varying degree, data relative to circuit, construction and operation of a light source which may be, without undue mental strain, related to the W. U. lamp of current vintage. Friederich utilized a tungsten filament to effect a "line source of light," which feature of the W. U. lamp has elicited such loud bravos from press commentators. Incidentally, Friederich actually showed but did not claim means for using his lamp as a rectifier — which claim the enterprising Meikle lost no time in staking out. This claim was subsequently adjudicated and held valid in a court ac tion in which General Electric was the plaintiff. Also providing interesting reading is a disclosure made in 1919 by J. K. Elderkin (Forest Manufacturing Corp.) . This relates primarily to a rectifier lamp but also shows specifically a corollary use as a "point source of light." This disclosure, prescribing the use of "any metal, preferably tungsten," anticipates the W. U. lamp in that it shows the same means for starting the lamp on high voltage and then cutting it off to operate a "pointed electrode" on low voltage. The only variance between the two light sources is the shape of the electrode. R. T. Cloud's Prophetic Patents However energetic and imaginative were these early workers, it remained' for one Raymond T. Cloud, as early as 1933, to forecast with pinpoint accuracy almost the exact principles which 13' years later were to gain for the W. U. lamp such widespread, if undiscriminating, kudos on the score of "originality." The portentous story is told in the following U. S. patents: 1,898,032— Cloud (Feb. 21, 1933) 1,905,153— Cloud (April 25, 1933) It would require considerably more effort than is involved in straining after the proverbial gnat to detect any but the most minute difference between the Cloud lamp and the W. U. unit; "identical" is the only acceptable term for describing the relationship of one lamp to the other, step-by-step from conception down to the finished product and its method of operation. Cloud shows specifically and in great detail all those elements which have led the unsuspecting to classify the W. U. lamp as "unique": 1 "The W. U. Concentrated-Arc Lamp," I. P. for April, 1946, p. 16. 2 "A Crystal-Gazer at Work," I. P. for June, 1946, p. 12. 14 CLOUD'S CONCENTRATED-ARC LAMP Left: side elevation of preferred form of lamp with the electrodes in perspective. Right: medial vertical section, showing the bulb and electrodes of sketch at left. The glass envelope itself; the character and positioning of a cathode, an anode and a starting electrode; the use of a molten oxide having a high melting point which is contained in a tiny recess in a holder; utilization of a high-potential power pack for starting, with subsequent low-voltage operation; effective shielding of the incandescent area to restrict light emission; specific mention of "any refractory material" (which W. U.'s zirconium certainly is) — right down the line Cloud delineates precisely the same type light source as represented by the, W. U. lamp. Cites Reproducing Application Cloud's primary objective, of course, was the production of a sound-film recording lamp; but he raised his sights materially in the following specific language: "The invention is not limited to recording, since without modulation of the light, as by voice currents, its constancy and brightness are ideal for a lamp for reproducing (italics ours). In such case the amount of light or intensity required will indicate a larger bright are*.. . . ." The fact that Cloud stressed the use of barium oxide, as compared with W. U.'s use of zirconium oxide, is as Tweedledee compared with Tweedledum, since Cloud specifies the use of "any metal oxide having a high melting point". Mere reference to easily available critical tables of substances and their melting points hardly constitutes initiative, much less "invention". Relative to the "point source" of the respective lamps, the Cloud specifications provide for a light-emitting area of from l/6,000th to 1/10,000 inch, and he demonstrates his capability of obtaining successful operation within these dimensions. Naturally, it follows that the larger the crater size the less concentration of light there will be on a given point. Cloud further cites the results of photometric tests which indicate for his lamp a brightness of approximately 100 candlepower per square mm., as contrasted with W. U.'s own published figure of about 56 c.p. (and other investigators' figure of about 46-50 c.p.) per square mm. for the zirconium lamp. The fact that the W. U. 2-watt lamp shows a higher brilliance than does its 100-watt unit (70 c.p. as against 50 c.p. per square mm., respectively) invites speculation anent the possibility of radically decreasing brilliancy per square mm. with increasing size and wattage. Contrast these figures with the 550 c.p. (Continued on page 26) INTERNATIONAL PROJECTIONIST • April 1947