The book is sometimes referred to in various spellings and formats, such as Linear Electric Circuits / [by] Wallace L. Cassell or Linear electric circuits / Wallace L. Cassell . This consistency helps confirm you are looking for the correct, authoritative source.

: A digital copy is often available for "checkout" through the Open Library project

I searched for but could not locate any publicly available, legitimate PDF of a textbook by that exact title and author. It's possible the title or author name is slightly different, or the book is out of print and not widely available in digital form.