ABSTRACT
Like you, I have read that Mr Parent has written about the thrust of vaults, archivolts, keystones, counter-keystones, and their action on their piedroits, and that they determine their force, depending on their weight and thrust; I am also aware that in his treatise on mechanics, Mr de la Hire has also demonstrated the arrangement that the archivolts of a vault can be given to make it durable, and that he has established the exact rules for finding the strength that the piedroits or supporting walls must have to resist the thrust under any and all circumstances. After that, my dear Colleague, according to you it is no longer permissible to attempt new research, nor to employ new means; operating on other principles would be to risk or, to put it a better way, to work towards the collapse of a building . . . to these new discoveries, to this profound study, to acquired experience, and to the careful calculations of Mr Soufflot we are going to owe the construction of a dome that will prove to posterity the progress that we have made in our time in the art of building, by casting aside the slavish principles to which, before him, all vaults and domes seemed to be subjected, and I confess in good faith that until then I had believed in the observations and theories of Parent and de la Hire . . . and if the reason of construction requires variety, then why should one want to make a dome, and the means to build it, a dogma, a determined axiom, and deprive it of the arbitrariness that is the wellspring of genius, masterpieces and discoveries? . . . It seems to me, however, considering the treatise that you have printed, based on his principles (first plate, first figure in your Dissertation on the dome of Saint Genevieve), that this dome or this so-called rule does not produce a fine effect on the proportions of a church, neither inside nor outside. That may be because the roof of the church on which you are planning to build it requires it to have a better, stronger and more elegant form. In truth, my dear Colleague, how can one presume to forbid rules, when the means of rejecting them are so weak (how can less than nothing be extracted from nothing)? For rules can be false or lost only if, for the project as a whole, the good effect of any edifice, the optical point from which it must be seen, comes into conflict with how they are used. After that, how must one operate? You do not know, and neither do I; for Fontana has mentioned nothing about it; and if he had, you would have as well.
