How to view more than one photo?

To view my photos, I generally go into the "Photos" part of the library and then just click the arrow for whatever given date of photos. Until a few days ago, when a date opened I had 3-4-5, maybe even 6 photos in a line across. Now, the photos are so large I can only see one at a time in the window. I can get to two in a row if I open the window as wide as possible. I don't know what I did to change this, but can't figure out how to go back. How can I see more smaller photos in a horizontal row?

Any ideas?
Thanks !