Use Oxford Music Online or the New Grove Dictionary of Music and Musicians (Carl B Reference ML100 .N48 2001) and search on the author's name and click on the article with his/her name. Review the article to find the following information:
Biographical information: Who is the author? Why did he/she write the work? When was it written or published? What was the prominence/influence of the treatise on other others or musicians?
Editions: What contemporary and modern editions have been published? What contemporary and modern translations have been published? Are there any modern facsimile editions?
Starting from the library catalog: Search for the title of the work to find modern and contemporary editions, including facsimiles. Search for the author's name to find modern and contemporary translations, including facsimiles. Remember that alternate titles may be used in these editions, so search carefully through the lists of works. If a book is not available at the Carl B, you can request it through Interlibrary Loan. Click on the yellow Request ILL button to initiate your request. Click here to view a tutorial on using Interlibrary Loan.
Starting from an Internet search: Search using both the author's name and keywords from the title. Use either the original title or the translated title, depending on which edition you are seeking. You will need to discern if the sites you find include the actual work, in either a facsimile (image) or full text. You will also need to discern the authenticity or accuracy of the text/image: What organization or individual has provided the text? Is the representation or translation of the work accurate? What is the source of the text/image?
You have several options for finding books and articles:
RILM Abstracts is one of the most used indexes for research in music. Much of the content is not available in full-text, so you will need to submit an Interlibrary Loan request for most of the books/articles that you find. Click on the yellow Request ILL button to initiate your request. Click here to view a tutorial on using Interlibrary Loan.
JSTOR is a collection of academic journals, including many prominent music journals. Articles are available in full-text.
Academic Search Premier is a general, interdisciplinary database that includes music and history journals. Much, but not all content, is available in full-text.
You can also search in the library catalog for books and articles on your treatise.
You can search in Google Scholar to find scholarly articles and books on your treatise. If articles and books are available through open access or are licensed by the Carl B, you will find PDF and FindIT links to the right of the title information.