xiv DESCRIPTION OF PLATES. 



PLATE XII. 



Fig. 156. The middle arch of Black Friars Bridge. P. 126. 



Fig. 157. A spherical dome, of which the lower parts are made thicker, in order 

 that they may be of equal stability throughout. From A to B the dome is of 

 equable thickness : below C and D the thickness cannot be increased sufficiently to 

 procure an equilibrium, without the application of a chain or hoop, of which the 

 section is represented at C, D. If the thickness were not at all increased, a hoop 

 would be required at E, F, or still higher. P. 127. 



Fig. 158. A section of the roof of St. Paul's Cathedral. The section of the 

 dome consists of two circular arcs, of which the centres are a little beyond the axis : 

 it is supported by carpentry, resting on a cone of brickwork. The internal dome is 

 of brickwork only, and is open at the summit. P. 127. 



Fig. 159. A section of the dome of the Pantheon at Rome. P. 127. 



Fig. 160. A Tuscan column, with its pedestal, capital, and entablature. P. 127. 



Fig. 161. A Doric column. P. 127. 



Fig. 162. An Ionic column. P. 127. 



Fig. 163. A Corinthian column. P. 127. 



Fig. 164. A Composite column. P. 127. 



Fig. 165. An elevation of the end of King's College Chapel, Cambridge ; show- 

 ing on one side the buttresses, the tower being supposed to be removed, and on the 

 other the tower, which not only supplies the place of a buttress at the end, but 

 assists also in supporting a considerable portion of the thrust in the direction of the 

 length of the chapel ; the roof, which is of stone, being vaulted in this direction as 

 well as transversely. There is also a roof of carpentry, covered with lead above the 

 stone roof. P. 128. 



