Letters arranged alphabetically by name of correspondent, mostly corporate correspondents such "Massachusetts Institute of Technology" or "American Institute of Electrical Engineers," but also some under the names of individual correspondents. Within the series are large sections of correspondence with Clarissa Hovey Thomson (Thomson's second wife), and also with John McManus, Jr., [identify]. As with any correspondent who has more than one letter in the series, the correspondence under those names are then arranged chronologically. In the cases where both persons corresponding were someone other than Thomson, both names were noted on the folder. In the cases of letters from institutions the name(s) of the individual representing the institution was also noted on the folder.

Arranged chronologically, contains materials related to the General Electric Company, but also material concerning the Thomson Houston Electric co., the Welding Co., patents (which were a GE interest) and letters or documents by persons not employed by GE but who somehow contributed to the work of GE. Documentation of scientific clubs by or for GE employees are also in this series, and also correspondence about GE publications. Since Thomson was so often consulted by other scientists and laypersons, it is difficult to distinguish between his work as a GE employee and his "personal" interests, often documented in letters addressed to him (and certainly answered by him) at his GE addresses. Series II also documents cases where the GE Company expressed a direct interest in technical or scientific institutions, meetings, trade congresses, technical terminology, acts of the U.S. Congress, and educational institutions.

Series I and II are accompanied by an index card file that has undergone several procedural changes since it was begun by APS librarians soon after the arrival of the collection. It began as a highly-detailed, item-level catalog for a portion of the letters that are now distributed between the two series, but that level of cataloging was impossible to maintain, and since one series is arranged alphabetically and the other chronologically, it is usually possible for researchers to use the two series together to find correspondents and then specific topics. The card file is also very useful for matching individual correspondents to their affiliated institutions, and since many of the cards contain a one-sentence snopsis of the contents they can help direct researchers to specific dates or correspondents.

Along with Thomson's incoming business correspondence, GE presented to the APS most of Thomson's outgoing business correspondence. Series IIA contains 43 large volumes, of which 28 are letterpress copybooks with hundreds of tissue paper pages while the remaining volumes are bound carbon copies of letters. Thirty-six of the letterbooks form one unbroken series extending from 1887 to 1936, while seven other letterbooks cover various periods from 1882 to 1890. Approximately six of the early volumes (1883-1890) contain only patent applications, interference briefs, and correspondence with the Patent Office. It appears that the series contains nearly all of the letters Thomson wrote while associated with Thomson-Houston and General Electric and perhaps most of the letters related to the American Electric Company.

The early letterpress copy books, especially the patent correspondence volumes, contain copies of Thomson's handwritten letters and notes. Around 1885 Thomson acquired a secretary and a typewriter, so most of the subsequent letters were dictated and typed. Unfortunately, because the chemical transfer process used in the letterpress copybooks occasionally worked poorly, some letters in these volumes are faint. Also, since the bindings of most of the volumes have deteriorated badly, and since the numbering system(s) for the volumes has been inconsistent, researchers should rely on the volume list provided by Charles Fitti, which follows later in this finding aid. Also, please note that Mr. Fitti took as a sample Volume 46 to test the amount of duplication between the documents preserved in the letterbooks and the letters in Series I and Series II. He found that of the 800 pages 30% were duplicated in either Series I or II (10% in Series I; 20% in Series II). Those percentages may vary in other volumes.

Material dating primarily from Elihu Thomson's years at Central High School in Philadelphia through the end of his life, although there are several files collected by his wife which date after his death in 1937. The series is arranged alphabetically by subject. Files consist of a variety of materials, such as legal documents, reports, specifications on inventions and patents, blueprints, programs for scientific meetings and events, and miscellaneous manuscript data relating to Thomson's industrial research and personal interests.

Subjects files hold much information regarding Thomson's inventions as well as his studies in astronomy, optics, and x-rays. Many of Thomson's early legal agreements relating to the development of the Thomson-Houston electric companies and the use of his patents have been preserved in this series. These documents trace the growth of Thomson's business concerns and his affiliation with early electric lighting companies such as the American Electric Company. Information on Thomson's involvement with many professional societies for electrical engineers and scientists is available throughout many of the subject files; as an active member of the Franklin Institute, the American Philosophical Society, and the American Institute of Electrical Engineers, Thomson collected much material on their meetings and events.

Autograph and typescript drafts, notes, comments, and printers' page proofs. Printed articles, journals, reprints, and photostats have been moved to the Thomson Reprint Collection. Title pages or first pages of this printed material were photocopied onto acid-free Permalife bond paper and included in the manuscript files before the printed material was transferred to the reprint collection. The only printed materials not removed from Series IV are several ephemeral pieces which are extremely fragile due to age.

Manuscripts of Thomson publications are arranged alphabetically by title, and focus on his lifelong interests in electrical systems, welding, astronomy, optics, etc. Many facets of Thomson's professional career and inventions are documented throughout the series. The manuscripts date from Thomson's first published article, "The Triumphs of Science" in his high school paper (1869), to the works published towards the end of his career. Besides manuscripts of papers prepared for publication in scientific journals, this series also contains manuscript drafts of Thomson's many editorial pieces published in both newspapers and journals throughout the country.

Comments by Thomson appear on separate sheets and on the actual manuscripts and evaluate the historical importance of many publications. It appears he was making these notes to a future editor of his biography/bibliography.

School papers, autobiographical essays, poetry, short papers on ideas and inventions, and any works which were not identified as published. These manuscripts are arranged alphabetically by title and date from Thomson's high school years to the end of his life.

Among the many high school papers preserved in this series, probably of most interest is the "Universal Journal." Produced by the Junior Scientific and Literary Society of Central High School in Philadelphia, this journal is primarily written in Thomson's longhand. Other manuscripts of interest in this series include the many short, anecdotal papers written by Thomson about his childhood in Philadelphia and the origins of his studies in the sciences. While most of these papers are autograph manuscripts, some appear to have been dictated to and typed by Thomson's second wife, Clarissa Hovey Thomson. A great deal of these autobiographical papers must have been used by David O. Woodbury in the biography, Elihu Thomson, Beloved Scientist (1944), as the stories are repeated throughout this book.

Manuscript and typescript drafts of speeches, lectures, papers and addresses given by Thomson at meetings of various professional scientific organizations and societies. The series also holds typed transcripts of these talks which were produced after they were given, as well as Thomson's preparatory notes and comments.

The speeches are arranged alphabetically by title. If a speech appeared in print at a later date, the title page of the printed version has been photocopied onto acid-free Permalife bond paper and filed with the manuscript material. The original printed material has been transferred to the Thomson Reprint Collection.

Manuscript and typescript drafts and transcripts of works by Thomson's colleagues and others and is arranged alphabetically by author. This series holds manuscript material both published and unpublished, including papers, reports, journal articles, speeches, and radio addresses. A large portion of the series is biographical, produced by Thomson's friends and colleagues after his death and originally stored in two boxes labeled "Biographical Material." The complete, original manuscript of David O. Woodbury's biography, Elihu Thomson, Beloved Scientist (1944), is preserved in this series as well.

Also of interest are several manuscript and typescript translations of historical works in the field of optics. Produced for Thomson's friend and fellow amateur telescope maker George Wattson Hewitt by Florence C. and Emil P. Albrecht, these translations date ca. 1901 and focus on the works of S. Czapski, J.J. Littow, and L. Schuppmann.

Thomson's high school notebooks from classes taken as a student, some industrial research notebooks, genealogy notebooks, and trip journals. Notebooks are arranged alphabetically by subject, although the folder title does not reflect all the information located in the notebook. Many notebooks contain miscellaneous, random notes regarding other topics. Often these notebooks were labeled on the front cover by Thomson, including his evaluations as to the historical significance of the contents.

Notebooks often appear in a journal or diary page format, although they were not necessarily used as such; often volumes printed as journals were used as notebooks, with no apparent connection between printed dates on pages and manuscript notes. In many cases, blank pages remain throughout the volumes. Miscellaneous diagrams and sketches appear within the text of the manuscript notes. Some of the journals documenting Thomson's travels contain additional notes in the hand of Clarissa Hovey Thomson, his second wife and traveling companion during the later years of his life.

Primarily pencil sketches of inventions and mechanical apparatus on individual sheets of assorted shapes, sizes, and types of paper. For the most part, sketches remain in Thomson's original order, as found in his filing cabinets. These sketches are arranged alphabetically by general subject headings and then chronologically within each file. In many cases, these sketches are only identified by date, without any other description. For this reason, they remain under Thomson's general subject headings, as they have not been identified any further. Other individual sketches are filed by subject when they have been identified. Occasional Thomson manuscript notes on specifications for patents appear on the sketches.

Several files of sketches by E.W. Rice, Jr., fellow inventor and business associate of Thomson, exist in a general chronological arrangement; most of these sketches are not identified by subject, but were found within a file labeled with Rice's name. Many of these sketches seem to have Thomson's manuscript notation on them and suggest collaboration between the two. Other sketches which appear to have been executed in conjunction with colleagues are identified by various signatures and initials.

Thomson's manuscript comments and notes on his patents. Originally bound in five volumes, comments are now arranged chronologically (by date patent was issued) on individual 8" x 10" sheets of paper. Each patent comment appears on a single page which has been laminated with Japanese tissue and is filed in a separate folder. Patents have been assigned identifying numbers which appear at the top of each patent comment and on a typescript list which duplicates the chronological arrangement of the series. This list is located in Box 1, Folder 1. Folders 2-4 in Box 1 contain typescript versions of the manuscript patent comments, and also follow the same chronological arrangement of the series (these typescripts exist for "vols. II-V;" "vol. I" is missing).

In these patent comments, Thomson describes and evaluates each invention, often detailing the slight variations and improvements in newer versions. Thomson continued to work on some devices for years; consequently, he held many patents for mechanical apparatus such as dynamos, electric lighting systems, meters, and lamps. Initials at the top of each patent comment sheet appear to refer to the individuals, often besides Thomson, who worked on the patent. Edwin J. Houston and E.W. Rice, Jr. most often appear as collaborators on these inventions.

Only three patent certificates issued to Thomson by the United States Patent Office have been preserved in this collection. They date ca. 1879 and are filed in Series XII, Certificates.

Black and white photographs in various sizes, organized alphabetically by subject or last name and then chronologically within each file. Besides early 20th century prints, several 19th century formats exist in this series as well, including albumen and cyanotype prints. Dates on the folders often reflect the date of the image, not when the photograph was taken, as this was sometimes the only date recorded on the photograph. Negatives can be located in this series as well; if a negative exists within a folder, [neg.] has been indicated after the folder title.

Photographs are often those of Thomson, family members, professional associates, events, and places. Many photographs of Thomson's inventions and miscellaneous mechanical apparatus are filed in this series as well. A typed description of the device often appears on the photograph, with a date reflecting the year of invention, not when the photograph was taken. Other photographs of interest include those taken by Thomson as a hobby.

Certificates which recognize Thomson's membership or election to many professional scientific organizations throughout his career. Certificates are arranged alphabetically by organization title. Also of interest in this series are three patent certificates issued to Thomson by the U.S. Patent Office.

Individual clippings arranged alphabetically by subject and scrapbooks of collected clippings (#1-4). Clippings have been photocopied onto acid-free Permalife bond paper; copies were filed and original clips were discarded due to brittleness. Topics of clippings include obituaries (of Thomson and colleagues), wedding announcements for Thomson's second marriage, and miscellaneous biographical information on Thomson and his career.

Scrapbooks primarily contain newspaper clippings, although a small amount of memorabilia and photographs exists within the scrapbooks as well. Some of the clippings in these scrapbooks are duplicates of individual clippings which have been filed by subject. For the most part, the scrapbooks follow a general chronological arrangement. For conservation purposes, these scrapbooks will be microfilmed in the future.

Miscellaneous items collected by Thomson, his wife, and the original organizers of this collection at the APS. The series is arranged alphabetically by subject or name of item. Several pieces of interest in this series date from Thomson's youth, including his birth certificate (1853) and his Philadelphia Central High School commencement program (1870).

Comprised of two subseries. Subseries A contains correspondence generated during the APS Library's attempt to collect Thomson letters from his colleagues after his death. It was the intention of those involved to create the most complete collection of Thomson papers possible; this meant writing to a great many prominent scientists and engineers across the country, asking them to donate any Thomson letters they may have received from him during his lifetime. Major correspondents of this series include Gertrude D. Hess, Assistant Librarian of the APS; Clarissa Hovey Thomson, widow; Roland S. Morris, APS President; Owen D. Young, Chairman of the Board of the General Electric Company; and John A. McManus, Thomson's longtime secretary at General Electric. Correspondence has been placed in five file folders and remain in its original, semi-chronological arrangement.

Subseries B holds inventories of manuscripts which were produced as the papers were donated. Several of these inventories record the various shipments of papers as they were received from Thomson's widow at their home in Swampscott, Mass. Other inventories were created as the initial processing of the professional correspondence occurred ca. 1937-38.

Both the correspondence and inventories of Series XV offer a great deal of information on the provenance and initial organization of the Thomson Papers at the APS Library.