How can I insulate these windows? I keep feeling like cold air is coming in from outside.

I recently purchased this 100-year-old house, and I love it. However, in the harsh East Coast weather, these old windows struggle to keep the cold air out. While it’s not a major issue, I’m taking steps to ensure we don’t feel the cold air seeping in.

Since the entire house is made of brick, it retains heat effectively. Additionally, the HVAC system is functioning well. However, fixing the windows would be a convenient solution to improve our comfort.

Thank you for your help!