(a) Method of making the uncoloured cylinders and spherules required for the study of the object picture.
An ordinary glass rod supplies the material for making the uncoloured objects we require.
Take a piece of glass-rod, hold it in a flame, preferably in a blow-pipe flame, until it fuses, then withdraw it from the source of heat and rapidly pull it out into a fine filament. The filament thus obtained will be a true cylinder. From such a filament an accurately figured sphere can be obtained by fusing its extremity in the fringe of a flame, allowing the melted glass to mould itself under the influence of surface tension.[1]
Fig. 2.
SHOWING METHOD OF MAKING A GLASS SPHERULE FROM A GLASS FILAMENT.
(b) Method of making the coloured glass cylinders and spherules. Select a pointed fragment of very deeply coloured window glass (avoiding ordinary ruby glass, which is only flashed with colour), and fuse the extremity of the fragment in the flame.
Having obtained in this manner a fused bead of coloured glass, seize this with a pair of forceps and, withdrawing the glass from the flame, pull it out into a filament. Introduce the coloured filament thus obtained into the fringe of a Bunsen flame, and allow the glass, as before, to mould itself into a spherical shape.
3. Arrangements for obtaining the different types of illumination required for the development of the outline and object picture.
The form of illumination which is required for seeing the spherule in the form of a picture in relief is obtained without any special arrangements. There will in each case be patches of light reflected to the eye from the surface of the spherule which faces the window, and in each case there will be an area of comparative shade on the far side from the window.
The varieties of illumination which are required for the development of the other varieties of object pictures can be conveniently
- ↑ For the purposes of our experiments it will be convenient to employ spherules not less than two millimeters in diameter and to leave in each case a portion of the filament attached in the form of a handle.
