About two years ago, while working at the crystalline form of a number of chemical substances of which I could obtain only small quantities, and in consequence minute crystals, I found that a great deal of time and trouble were lost in consequence of having the use of only one goniometer. When a crystal was fixed in its place by canada balsam and carefully centred,—a tedious operation when carried on under the microscope, as I had generally to do,— its angles measured and description noted, I found I often wanted to keep it for comparison, but before another could be examined, the first had to be taken off and half an hour spent before the second could be got into a satisfactory position, the first being very often spoilt in being removed, or even if still entire, much time must be lost before it can again be referred to. Now the possession of half a dozen instruments would obviate all this, but few chemists can afford the luxury of such a number of goniometers, and unfortunately so few possess one at all that it is seldom that such a thing can be borrowed.