While the original 1967/1968 editions are rare, you can access the material through several academic and archival platforms: Unified Theory Of Electrical Machines - mchip.net

Regarding your request for a PDF of "The Unified Theory of Electrical Machines" by C.V. Jones, I couldn't find a direct link to a freely accessible PDF. However, I can suggest some potential sources:

These books provide the as Jones, with clearer notation and modern case studies on PWM inverters and digital control.

The unified (or generalized) theory simplifies complex machine analysis by focusing on shared fundamental principles rather than treating DC, induction, and synchronous machines as entirely separate entities.

Designing control algorithms for modern industrial motors.