weight c d x a .
c d seems to press on the arch towards the abutment at the point p but the weight p o opposes resistence to it, whence the whole pressure is transmitted to the root of the arch. Therefore the foot of the arch acts like 7 6, which is more than double of x z.
II.
ON FISSURES IN NICHES.
777.
ON FISSURES IN NICHES.
An arch constructed on a semicircle and bearing weights on the two opposite thirds of its curve will give way at five points of the curve. To prove this let the weights be at n m which will break the arch a , b , f . I say that, by the foregoing, as the extremities c and a are equally pressed upon by the thrust n , it follows, by the 5th, that the