IS46.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



41 



RAISING THE SPIRE OF A CHURCH. 

 (From the American Franklin Journal.) 



" Account of the Raising of /he Spire of the Nativity, in Spring Garden, 

 Philadelphia county." By N. Le Brun, Architect. 



The Doric tower on which this spire was raised, faces the east, and is 90 

 feet in height ; it is strengthened at the angles by four buttresses, project- 

 ing at the base four feet ; the projection of these buttresses is diminished at 

 four stages in their height. The interior figure of the tower at the base is 

 a square, but mid-way it assumes the figure of an octagon by gathering 

 over the brickworli at the angles ; the whole forming a construction of the 

 most solid character. The octagonal spire, which was finished complete in 

 front of the tower previous to rising, is 80 feet high, including its crown- 

 ing ornaments ; its width at the base is 12 feet 6 inches. 



The spire was raised by means of two derricks situated on the north and 

 south wall on the top of the toner, and placed about 18 inches behind the 

 front posts of the spire, or about 3 feet back from the front of the toner, 

 and were 13 feet, 6 inches apart, allowing about 6 inches on each side be- 

 tween them and the spire. Their feet were made convex and fitted into 

 corresponding cavities worked in the oak sleepers which were securely 

 bolted down into the sills of the spire, which sills were themselves secured 

 to the tower by IJ inch rods 36 feet long, and built in the angles of the 



tower walls. To avoid all the strain being thrown on the top of the walls 

 at these points, diagonal braces were placed, extending 40 feet down the 

 tower, and as an additional precaution to prevent the derricks from slip- 

 ping at the heels, they were connected by la<.hings fastened to iron bolts 

 passed through them,— the heads were coniiccted by two tackle blocks, 

 which were only of use to keep them in their position till the spire was 

 being raised. The guys from each of the derricks, extended in three direc- 

 tions over the neighbouring commons. 



The spire was connected with the derricks by four double lashings, (each 

 end of which was fastened to one of the spire posts at the foot,) and two 

 spans ; the belt, which connected the spans, was 30 feet high above the base 

 of the spire, (being about 5 feet above the centre of gravity) and passed 

 through the straps of the purchase blocks. The falls from the treble blocks 

 on the derricks to the leading blocks, were in the interior of the tower, 

 and the two capstans used, were placed in the main story of the church, 

 and were each manned by twenty men. Attached to the base of the spire 

 were three guys, and at about 25 feet from the head were four more guys, 

 all secured to guy posts. 



All the arrangements having been made with the greatest care, on the 

 1 0th of February, at two o'clock in the afternoon, the raising was com- 

 menced, and it was performed with the greatest ease. The spire was kept 

 plumb by the management of the guys attached to it. As the derricks were 

 but 42 feet high, and the belt to which the purchase blocks was fastened 

 ■was 30 feet from the base, (at which height the distance from each der- 

 rick head to the spire would be about 3 feet,) there would be but 6 feet 

 between the blocks when the spire would be raised ; — they would thus 

 necessarily have lain almost horizontal, and caused a great strain on them ; 

 to avoid this strain, as the raising was progressing, the north and south 

 derrick guys were slackened to make the purchase blocks work more per- 

 pendicularly. 



When the spire had been raised to its proper height in front of the tower, 

 the two west derrick guys were worked by two crabs to draw over the der- 

 ricks and swing the spire to its destined position. It had been deemed 

 most prudent to work them in that manner, as in the hauling in of the 

 back guys in the usual manner, an oscillatory motion might have been com- 

 municated to the spire, which would have rendered it difficult to manage at 

 this most critical moment. The raising lasted an hour and thirty minutes, 

 and thirty minutes were required to secure it firmly to the sills onlhe tower 

 by the iron straps ; — thus the whole operation occupied two hours. 



METHOD TO PROJECT CIRCLES ISOMETRICALLY. 



By Thomas Prosser, C.E., New York. 

 Fig. 1. Draw the two Isometrical diameters ; {i. e. the two exi-conjugate 

 diameters of the ellipse which is to represent the circle,) unite their ver- 

 tises so as to form a rectangle with its diagonals ; circumscribe the whole 

 with a circle passing through each angle of the parellelogram, the sides of 

 which will thus form chords to its segments ; with the chord of half the 

 arc of a lesser segment as radius, describe another concentric circle cutting 

 the diagonals of the rectangle, at a, a, a, a. 



From each angle of the rectangle as centres, and with its largest side as 

 radius, describe arcs cutting each other within the rectangle as at b, b. 



6 



