So when you say “harnessing electricity” three things come to mind- generating electricity (wind, solar, fossil fuels, etc), batteries (harnessing in the sense of storing), and early investigations into what electricity actually is and how it can be used (Benjamin Franklin’s kite experiment, Nikola Tesla’s work, etc).
Here are some resources for each topic:
A write up/timeline about Ben Franklin’s experiment:
General history of electricity: this is a quick read, but touches on many topics of electricity (science, politics, economics, etc.) So depending on which sparks your interest, you can follow the references on each topic.
He did a ton of interesting experiments (including trying to transmit electricity through the air!). He is most known for developments in alternating current- which is the primary form of electric current you use in your day to day life.
Wikipedia has a list of a bunch of Tesla works: Tesla work.
Here is an interesting documentary about him:
Batteries: If you are at all interested in batteries, I recommend you glance through the following books- they are a bit lengthy, but they will tell you everything you ever wanted to know about batteries and then some. They are the Principles and Applications of Lithium Secondary Batteries and the Handbook of Battery Materials. These are pretty standard texts/resources in the battery industry.
A brief summary of electricity sources since 1950: electricity in the us.
A report from the National Renewable Energy Lab (NREL) outlining the current state of our energy supply: admittedly this is a bit tedious, and I know you asked for early studies on harnessing electricity, but this baseline report is a pretty good resource for someone interested in the area, so I figured it couldn’t hurt to share.