I agree that the windowsill is not always a good place for plants. The plants may received some sun during the day but they are also exposed to the cold temperatures coming through the un-insulated glass and if there are air leaks around the window the wind is like an ice cold blow torch.
If you can locate the plants on a table near the window and place a mirror to face the window, the mirror will direct some of the sunlight toward the plants.
Since the window sill is a cold place in your home, do you have fluorescent lights in your house? If so, you can put the plants (or the jar of water with cuttings) on a high place such as the top of a shelf or top of the refrigerator so the plants can be closer to the light. For example, in my house I have full-spectrum fluorescent lights on the kitchen ceiling, so during the winter I put my plants on top of the refrigerator, on shelves and on the floor. Each day I rotate the location of the plants so each will get some good light to keep them alive. During the winter months the kitchen is the warmest place in my house; it also has less cold drafts of air as it is far away from the front door.
