APPLICATIONS OF TIMBER. 189 



the durability has not been corresponding ; for- 

 the roof had to be replaced in 1802. The ori- 

 ginal architect was Sir Christopher Wren; and the 

 roofing was long considered as a masterpiece of 

 carpentry. 



The Basilica of St.Paul at Rome has a roof of large 

 dimensions, the span being more than seventy-eight 

 feet. It is framed of fir. The trusses are double, and 

 placed about fifteen inches asunder, which gives it 

 probably more stability, than if they were strapped 

 and bound into single masses. 



The Theatre d'Jlrgentino, also in Rome, is of still 

 larger dimensions, the span of the roof being more 

 than eighty feet. This roof is also of fir, and sup- 

 ports the weight of the whole machinery of the theatre. 



The number of roofs of large span that have re- 

 cently been constructed, is very considerable. Per- 

 haps one of the strongest is that of Drury Lane 

 theatre, which has a span of eighty-three feet and 

 three inches, within the walls. The trusses of this 

 roof are fifteen feet apart, and they are so judiciously 

 constructed, that each truss can bear a load of three 

 hundred tons. The roof of the chapel at Green- 

 wich Hospital, constructed by Mr. Wyatt, is one 

 of the finest specimens, and perhaps contains 

 less superfluous timber than most of the others 

 of the same span and carrying the same weight. 

 A new roof put upon the church of St. Paul, Co- 

 vent Garden, in 1796, also shews the progress of 

 modern art in this very important department of 

 carpentry. The trusses are as strong as those 

 in the original roof, contrived by Inigo Jones, and 

 yet each of them contains eighty cubic feet less 

 timber. Indeed, in no one department of the arts, 

 has the application of scientific principles tended 

 more to lessen the quantity of materials, than in the 

 construction of large roofs; and this has a treble 



