M. Lavoisier has asked the Academy's advice, in the name of the régisseurs des poudres, on the best way to reconstruct the Arsenal's powder magazine, and the Academy has appointed us, M. Franklin, M. d'Arcy, M. de Montigny, M. Perronet, M. Lavoisier and myself, to a committee on this subject. We are going to report our observations on this important matter to the Academy, as well as what we think to be the most advantageous course of action to follow.

The best-constructed powder magazine must not only be protected as much as possible from exterior and interior threats of fire and water, but it must also be built in such a way that, in the case of either of these accidents occurring, especially fire, the least possible amount of harm and damage is done; for as we know too well, despite every human precaution, these accidents occur.

With these concerns in mind, after having consulted with Messieurs the régisseurs about the proper location for establishing the new magazine, we had agreed that it would be built overhanging the arsenal's moat, above the highest water level as shown in the drawing, and that it would be built in the following manner:

In the form of a square, each side should have been 24 feet long, measured from the interior; the walls were to be 12 feet high from the ground floor of the garden over the entablature, and be at least 7 feet thick. The interior surface of these walls should have been in a straight line, but the outward facing was to incline toward the horizon so that the magazine would become widened or larger at the top than at the bottom, by a certain proportion. This funnel shape would facilitate the expulsion of the powder fluid in the case of an explosion. Instead of being straight, the interior surfaces of these walls were to be curved. In the horizontal direction, the concavity should have been facing outward, that is, in the arc of a circle with a 24-foot perimeter. These walls, raised perpendicularly, should have been flanked at each corner by a square block of masonry measuring 14 feet two inches. Finally, since in such a magazine, bombs need not be feared, the roof was to be lightweight and made of slate. That way, in case of an accident, the whole roof would blow off easily, as we know this is done in powder mills. All these details are made clear in the drawings of the plans and the elevations of this magazine, which the Academy has before them.

This was the construction that we had proposed to present to the Academy, and the different dimensions that we had agreed upon for the thickness of the walls, based on those which M. de Vauban had determined in the past and are still followed today.

But then we tried to examine what had given rise to the determination of these dimensions, on what ground they had been founded—the experiments which had been done on the resistance of the stones, and the force that gunpowder exerts in exploding— in sum, the different elements which require measured observations up to a certain point, to establish some certainty about the powder magazine's form, the dimensions of the walls, etc. We quickly realized that we did not have enough data to suitably solve a problem of this importance.

In fact, in the dimensions which M. de Vauban prescribed for powder magazines, this great man appeared to have followed only what his experience and good sense told him on the matter, especially with regard to the effects of bombing. However, he was unable to draw conclusions without more knowledge of the data required for the solution of this problem.

In view of these considerations and our various reflections on this subject, we thought that we could not give a response worthy of the trust which the Academy placed in us, until we had acquired more certain and profound knowledge of the elements mentioned above. It is to be wished, in consequence, that the government order experiments to be conducted, experiments necessary in order to acquire this knowledge. This would result in a great quantity of new and useful information, in a completely new subject on which no experiment has been conducted thus far. The tests undertaken made to measure the force of powder, and in particular those carried out by one of us, M. d'Arcy, have led us to hope for success in this research. Finally, the subject was of such enormous importance for the artillery and the public safety, given the large number of powder magazines spread throughout the kingdom, that it was of the greatest consequence to determine, on the basis of this information, everything that could lead to the discovery of the best method of building powder magazines. Read in the Académie des Sciences on March 26, 1779