368 SURVEY OF THE COAST 



These pillars go through the floor without touciung it, and 

 rest below upon a solid block of masonry, about six feet 

 high, firmly founded below the excavation of the cellar on a 

 base the breadth of which must be proportional to the soli- 

 dity of the material employed, of which the best would be 

 one solid block of stone. 



Upon a similar pillar q, somewhat on the side, to the south 

 east of the transit, the clock is to be placed in such a direc- 

 tion as to present the face about perpendicular to the desk. 

 The centre of the second hand must be made to come about 

 five feet eight inches above the floor, for the ease of reading 

 and to show below the transit. It can be easily illuminated 

 by a lantern placed on the side of the pillar near it, so as not 

 to throw any light to the eye of the observer, 



'I'he top of the pillar is regulated by the size of the clock, 

 and the base by the necessary solidity. It must be indepen- 

 dent of the floor, and have a particular shape adapted to the 

 clock, 'I'o admit the case to go round it, without enclosing 

 the pendulum in the stone, it may rest upon the same base- 

 ment as the transit, or upon a similar one equally solid ; but 

 there must be room made in it to admit the weight of the 

 clock, intended always to go below the floor. 



The complaint against the small cuts in tlie roofs of ob- 

 servatories is well known, and their influence, in a warm 

 climate particularly, in producing a local refraction near the 

 observer, would be too great. This was the reason for plac- 

 ing the ti'ansit in the direction of the windows, which will be 

 opened entirely for observation. 



The part above the window, up to the roof, presenting 

 itself outside like a continuation of the wall, fig. 3, e, e, must 

 also open completely, like an inside shutter. 



The roof over the transit between the two windows must 

 slide out to both sides upon the other roof for the whole 

 breadth of the windows. It is composed of five double shut- 

 ters of strong sheet tin, moving on round iron bars^, g lying 

 on the roof, and reaching far enough in the cut to give a solid 

 support to the shutters ; and if small, they might go entirely 



