Edison U.S. Patent No 444,530 (and Reissue No 12,393)

Edison's Patent No 444,530 deals with the leading-in wire. The patent figures appear below.

Fig 3 represents the Edison stem press as manufactured in 1889. Fig 1 represented the stated preferable design being patented whereas Fig 2 represented an alternative acceptable design. In Fig 1 the length of the platinum wire was reduced to a length of 1/8th of an inch. Four welds were embedded in the seal region. In time, however, it was found that Fig 1 was not the preferable design for the reason that "the copper wire was not found advantageous to clamp the filament to, and was abandoned as a clamp wire after many inferior lamps had been made" (J. T. Marshall, "The Development of the Manufacture of the Edison Incandescent Electric Lamp - 1881-1905," Journal of the Franklin Institute, Vol 160, 1905, pg 28). However, the design in Fig 1 was used from 1890 to 1894. It is surmised that the advent of the carbon paste joint was a welcome relief from the arduous plating required with the copper inner lead; the new procedure, shown in Figure 2, was also less expensive than the old one. In 1894 the design shown in Fig 2 was adopted for use in manufacturing Edison lamps. The method remained in use as long as carbon filament lamps were manufactured.

The U.S. Patent No 444,530 was applied for Sep 15, 1890 and was issued Jan 13, 1891. It was reissued; the application was filed Jul 12, 1905 and reissued Oct 10, 1905. However, on May 14, 1908 the patent was declared invalid, on the grounds that the wire arrangements simply provided a mechanical improvement (Electrical World, Vol LI, No 21, May 23, 1908, pg 1084). It was also claimed that Heisler had used the joint "before the period which the patent was claimed to cover." It was a unimportant point, however, as the patent had already expired (in Jan 1908).

As it concerns this patent, the writer is confused about statements made by Arthur A. Bright, Jr. (The Electric-Lamp Industry: Technological Change and Economic Development from 1800 to 1947, The Macmillan Company, 1949.) On pg 125, and then again on pg 205, he referred to the three-part leading-in wire as the "Siemens" seal. It would be of interest to determine if Siemens had their own seal or whether it was the same as the Edison seal. It would be appreciated if a knowledgeable viewer of this site could clarify this issue for the benefit of the writer and lamp collectors.