My attention was first drawn to the change of volume which takes place when a salt is dissolved in different quantities of water, by an experiment shown by Sir William Thomson in his class at the Glasgow University. He took a wide glass tube, about 3 feet long, sealed at one end, and having a narrow tube attached to the other end. The lower half of this tube he filled with a saturated solution of common salt, and on the top of that he placed a layer of water, which just reached a mark about the middle of the small tube. He then corked the open end, and mixed up the water and brine by inverting the tube two or three times, when it was seen that the solution had contracted.