The other mode of forming common tourbillons, is the following: They are made with cases of an inch, which are choaked and bound in the usual manner. In filling, we make two wads of paper of the same size, and put one of them into the case, and ram it with fifteen or twenty blows. We then mark upon the case, the height of this wad, which is afterwards driven with the composition, given at the end of this section. To each charge, thirty strokes of a moderate size mallet, will be required; and each charge should not be more in height in the case than nine exterior diameters. We mark, on the outside of the case, the height of this charge, and put in a wad of the same kind and size as the former one. We drive this in the same manner as the first, and then choak and bind the case. After cutting off the excess of the ligature, with which we bound the case, we again introduce the rammer, and give it eighteen blows with the mallet, in order to flatten the choak.
We afterwards divide the case parallel to each end, into four equal parts, and mark the height of the wads. That of the middle, which becomes in fact the bottom of the case, (from the manner it is fixed for ascension), we divide into five equal parts from one point to the other, and pierce a hole in each division to the composition. We then make, on a level with the wads, upon the lateral lines, two similar holes; one upon one side, and the other on the other side, at the opposite ends. These holes are so made as that the case has four holes on one line, and one upon each of the other two. Each hole is then primed with a piece of quick match, and priming paste. One of these matches must pass over all the other holes; so that the fire may be communicated from one to the other at the same time. The matches are then covered with a band of pasted paper. To hold the tourbillon in a horizontal position, we procure a hoop of the same thickness and diameter as the length of the case; and on the plate, we make a groove for the match of communication, which is supported between the four holes with an iron wire. If the case whirls round with a uniform motion, it is well balanced.
The four holes beneath, serve to raise it in the air, and the two lateral apertures give it a revolving motion.
When tourbillons are to be set off, they must be balanced either by a cross stick, as in the first instance, or some other contrivance. The effect is the same as before described.
Composition for Tourbillons, or Table Fusées, of different Calibers.
| Substances. | Calibers of ⅓d of an inch. | Of ⅔ds of an inch with Chinese fire. | Of 5/6ths of an inch with Chinese fire. |
| Saltpetre, | 8 oz. | 16 oz. | 16 oz. |
| Sulphur, | 4 oz. | 8 oz. | 8 oz. |
| Meal-powder, | 16 oz. | 18 oz. | 16 oz. |
| Charcoal, | 1 oz. | ||
| Pulverized cast iron, | 10 oz. | 12 oz. |
Another composition for a caliber of half an inch, of common fire.
| Saltpetre, | 16 | oz. |
| Sulphur, | 4 | — |
| Meal-powder, | 7 | — |
| Charcoal, | 4 | — |
The following formulæ are sometimes used;
For four-ounce tourbillons.