370 a^URVEY OF THE COAST 



the wall nor any of the pillars ; the joints being covered with 

 cloth nailed to the floor to prevent the draft of the air from 

 the cellar. The under part of the floor is plaistered lil<e a 

 ceiling, in order to prevent more effectually the dampness. 

 and make it a more compact body or mass. 



The cellar must be about five feet deep, as well to pre- 

 vent dampness under the floor and about the pillars, as to 

 admit easy access to these, and beneath the floor, in any case 

 of need. For the same reason also, the bull's eye windows 

 are given to it in the southern and northern front. The ac- 

 cess to it may be under the step which leads to the upper 

 room, and under the main door and the bridge before it a 

 door may be made to come into the ditch. 



The ditch around the building must be at least four feet 

 deep, and about three feet in breadth, to intercept all oscil- 

 lations of the surface of the earth which may be occasioned 

 by wagons, ^c. particularly in cities or near inhabited places, 

 roads, ^c. This of course renders necessary a light bridge 

 passing to the door. • 



The roof is arched, and elevated about twenty feet above 

 the floor, to avoid all close air under any circumstances what- 

 ever. 



Instruments which would reach into the upper heated air- 

 of a room would never make a good observation, particular' 

 ly in such a variable climate as this. 



My plan for the framing of a roof may be seen in the 

 figure. In the arrangement of the rafters, it was necessary 

 to pay attention to the opening in tlie roof that might be re- 

 quired for the additional instruments mentioned above. 



