Below you can see the front-view size comparison of the Olympus E-M10 II and Nikon 1 S1. The Nikon 1 S1 is clearly the smaller of the two cameras. Its body is 18 mm narrower, 22 mm shorter and 17 mm thinner than the Olympus E-M10 II.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.