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Over the years, a variety of numbering systems have been employed by Edison and others to identify the notebooks used in the West Orange laboratory. Many of the standard-size (6" x 9") books have a small numbered label on their spines. These labels were probably affixed to the books in 1903. Books 2-35 were generated during the period 1880-1886. These books appear in Thomas A. Edison Papers, Part II (1879-1886). Book 1 and books 36-143 were generated during the period 1887-1895. About 75 technical notebooks dating from the period 1887-1895 lack spine numbers, including most of the books used exclusively by Edison.
In addition, there are about 75 notebooks, most of them used by experimenters other than Edison during the period 1887-1892, that contain a number affixed to their front covers. These numbers range from 494 to 641 and do not seem related to the numbers on the front covers of the notebooks used prior to the opening of the West Orange laboratory. Unlike the spine numbers, these numbers were probably affixed to the books before they were put into use.
Beginning in the late 1930s, the archivists at the West Orange laboratory began assigning "N-numbers" to the standard-size notebooks. This six-digit number generally corresponds to the first dated entry. For example, a book whose first dated entry is from May 9, 1887 carries the number, N-87-05-09. Books with the same N-number are distinguished by an extension number; for example, N-87-12-08.1 and N-87-12-08.2.
The N-number is not always reliable as an indicator of the date that a book was put into use. Some books were used for a long period of time before an entry was dated. Others contain no dated entry. In such cases, a conjectured year serves as the first two digits of the N-number. For example, a book that probably dates from 1887 would carry the number, N-87-00-00. Subsequent research has revealed that some of these conjectured years are inaccurate. A few undated books are so problematic, that no effort has been made to assign a year. Such books are indicated by the notation, "N-Undated," plus an extension number.
The N-number system is the only one that was consistently applied to all the standard-sized books. For that reason, the notebooks are organized in N-number order. Pocket notebooks, which contain similar six-digit numbers preceded by the designation, "PN," appear in PN-number order. Since form, rather than content, determined which bound volumes would be assigned N and PN numbers, not all the books so designated are experimental, or even technical, in character. Items with these numbers can also be found in the Laboratory Records Series; the Alexander Elliott, Jr., Papers; and the New Jersey and Pennsylvania Concentrating Works Series.