A SILVERED GLASS TELESCOPE. 



45 



ever, to let it rest on the edge h h", when not in nse. At r there is an iron catch 

 on the arch, bywhicli tlie lever e, that raises the dome, is licld down. The fulcrum 



Fig. 40. 



rig. 41. 



'I'lie Dome Arch. 



is at d. The lever is hingt'd near c, so that when by being depressed it should have 

 come in the way of the telescope below, the lower lialf // can be pushed up, the 

 part from c toward d still holding the dome supported. 



The arch can be set across tlie observatory in any direction, north and south, east 

 and west, or at any intermediate position, because tlie alintments \\licre tlw ends 

 rest, are formed by a ring / /' /", fastened round the circular aperture, through the 

 stationary part of the roof 



AVhen the teh^scope is not in use, and the dome is let down, so tluit there is no 

 longer an interval of a quarter of an inch between it and the rest of the roof, it 

 is confined inside by four clamps and wedges. Otherwise, owing to its lightness, it 

 would be liable to be blown away. These clamps «, 

 Fig. 41, are three sides of a square, made of iron one 

 inch square. They catcli above by a ])oint in the 

 wooden basis-circle of the dome /*, and below are 

 tightened by the wedg(^ r. 



When the dome is raised it is prevented from moving 

 laterally and sliding off by three rollers, one of which 

 is seen at _/', Fig. 40. These catch against its inner edge, 

 and only allow slight play. At first it was thouglit ne- 

 cessary to have a subsidiary half arch at right angles to 

 the other to hold it up, but that is now removed. 



All the parts work very satisfactorily, and owing to 

 the care taken to get the roof-circle and basis-circle fiat and level, no leakage takes 

 place at the joint, and even snow driven by high Avinds is unable to enter. 



c. TJie Observer's Chair. 

 This is not a chair in the common acceptation of the word, but is rather a movable 

 ])latform three feet s([uare, cai)able of carrying two or more persons round the 

 obser\ atory, and maintaining tliem in an invariabk- position with regard to the tele- 

 scope eyepiece. 



A Dome Clamp. 



