I have a cat and a dog the cat is terrified would it help getting another cat?

We have had an adorable little cat Sonny for about a year and a half. She was great but our family decided to get a dog. A month has passed since we rescued our 10 month old Lab/Beagle mix ,Lucky.Their first experience was that of a chase. There were many more like this as long as the cat was on the move, but if the cat was at the window staying still a couple barks and Lucky calmed down. As for when the cat is running we are truly scared the dog may injure the cat. Then we thought getting another cat might help but were not sure. If you have any ideas on how to get these two animals living with each other please answer any help is appreciated!! Thank You!!