" On Saturday, the :30th of September, Course XXVIII. was completely set ; and, being the first course upon which was rested the vaulted door, which made the ceiling of the store-room and floor of the upper store-room ; as here again occurred a ditlerenee in the mode of fixture, in this, as in all like cases, I attended the performance of the work : and that was the leading-in of the first circular chain, that was lodgoil in a groove cut round the middle of the upper surface of this course, M hich this day was satisfactorily pet' formed ; and the next day, Sunday, October the 1st. Course XXIX. was set, and its circular chain leaded-in also ; • which operation, with the reason thereof, it will be proper here to describe : The ordinary way of fixing the several bourses by joggles and joint-stones, and also the bonding them together by cramps, has already been described ; but those courses, upon which the floors rested and depended, seemed to demand every possible security. It will be seen, in the general section. Plate II. that each floor designedly rested upon two courses : it NVIII also appear, by inspection, that the circumference of the floors was not made to rest upon the sloping abutments of en arch, in Hues tending toward the centre of the sphere, of which the under side of the floor was it portion, but it rested upon a triple ledge going circu larly round the two supporting courses. In consequence of this, had each floor been composed of a single stone, this lying upon the horizontal bearings furnished by these ledges, would, while it remained entire, have no lateral pressure or tendency to thrust out the sides of the encompassing walls : and that in effect, the several pieces, of which the floors were really composed, might have the same property as whole stones, the centre-stone was made large enough to admit of an opening, from floor to floor, or man-hole, to be made through it ; and being furnished with dovetails on its four sides like those of the entire solid. it became the means by which all the stones in each floor were connected together ; and consequently, the.whole would lie upon the ledges like a single stone, without any tendency to spread the walls. But if, by the accident of a heavy body falling, or otherwise, any of those stones should be broken, though this might not destroy its use as a floor, or its properties as an arch ; yet the parts would then exert their lateral pressure against the walls: and therefore, as a security against this, it became necessary that the circle of the enclosing walls should be bound together, and the building, as it were, hooped.
" This would he in a great measure brought about by the cramps tying the neighbouring stones together, as already described, for the ordinary courses ; but yet this was no absolute security, because the outside stones might break and separate, between cramp and cramp : and I suppose, it was for reasons of this kind, that Sir Christopher Wren, in the construction of the cupola of St. Paul's, did not choose to depend upon cramping the stones together, of the course that served as a common base to the inside dome, and the cone for supporting the lantern ; but chose to surround the whole with continued chains of iron. Upon this principle, an endless chain was provided fbr each of the two floor courses; see Plate IV. Figure 7. The bars composing the links being one inch and a quarter square, that the most iron might be included in a given space, the corners only were a little canted off ; and the double parts being brought near together, the whole was comprehended in a groove, of some what less than four inches wide, and as much in depth; into which the chains being introduced and brought to a stretch, the rest of the cavity was filled with lead, of which each took about eleven hundred weight, in the following method. The chains were oiled all over before they came
from the shore ; and the circumference of the groove was divided into four parts by stops, or dams of clay, to prevent the lead from flowing farther than one quarter at a time. A couple of iron kettles were provided, capable of melting com modiously, when full, six hundred weight of lead each ; and that quantity was brought in each to a full red ; that is, somewhat hotter than we used for the cramps, as the iron of the chain, as well as the stone, were cold. The whol9 quantity of lead being brought to a heat that we judged proper, and the quarter-groove being supplied with oil suffi eient to besmear the whole surface, two persons, with each a ladle, as briskly as they could, poured the melted metal into the same quarter of the groove ; and, as soon as it was full, and the lead began to set, one of the clay dams was removed, and the melted hut metal was poured upon the end of the former mass, till it was perceived to re-melt and unite with the fresh metal. This done, the dam at the other end of the first-run mass was taken down, to prevent its cooling more than was necessary, and the third (mailer was treated like the former ; the end of the mass rendered solid by cooling, being re-melted by the fresh hot metal : lastly, both the remaining dams being taken down, and the metal at each end having a considerable heat, it was found practicable to dis solve both the ends of the firmer masses : first applying both ladles to that which had had the greater time to cool, and afterwards to the less : by this means the whole was brought to a solid consistence, and the chain entirely buried in the lead. It is, however, to he remarked, that to preserve proper impressions in the lead, for the joggles of the course above, those impressions were made by confining down bricks in proper places, which, when removed, the proper marble joggles were set with mortar in their places.
" Monday, October 2, we proceeded to set up the centre, composed of sixteen ribs, (see Plate VIII. Figure 3.) for putting the floor together upon ; but the weather continued broken till Saturday, the 7th, on which day the Eddystone boat came out, haying on board the roof, or platfbrin, for covering the building, and protecting it from the entrance of the downfall spray ; together with the doors, iron work, and timber for fitting up the same for habitation. This afternoon we landed, and went on with the setting of the outward circle of floor-stones, made the holes in the wall for fixing the hinges of the entry and store-room doors. In particular, caused the middle stone to be laid upon the centre, by way of weight, to keep it steady. Three of the four stones that were to connect with the centre-stone were laid upon the top of the wall, on the north-east side : and the fourth I caused to be hoisted and suspended upon the triangle, in the posture that is shown Plate VI. at stage second. So that the triangle, which was all of it completely within the area of the top of the building, would be kept down by the weight of this stone, which was between seven and eight hundred weight. The other three that lay upon the wall, I caused to be carefully drawn within the circumference thereof, so that there might not be the least projecting part for the water to strike against in flying upwards ; which I judged quite necessary, though the walls were then upwards of forty-three feet above the foundation-stone, and near thirty-five feet above the top of the rock." The weather now set in so bad, that no farther operations of consequence took place that season. On the 10th of October, Mr. SmeatOn was mortified with a copy of a reso lution of the Trinity-Board, declining his proposal of exhibit ing a light that winter upon the foundation of the building.