A Cheap Observatory. 245 



The larger circle is ten feet and the smaller eight feet in 

 diameter. The latter was mounted over the former on the four 

 uprights,, and the cross beams laid in their places and well 

 secured. 



The sides were then covered in with light deal boards, 

 the edges of which being ploughed and tongued the joints 

 were rendered quite close aud perfect, at the same time they 

 were securely nailed to the elm circles above and below. 



For the greater comfort of being well inside the building 

 when observing, instead of the front shutter being formed on 

 the sloping surface, it was thought better to carry the cross 

 beams, on one side, some distance beyond the edge of the roof, 

 to be met by uprights standing vertically on the lower elm 

 circle, the intervening surface being boarded up and forming 

 a kind of porch. A window also was inserted on the right- 

 hand side of the porch, for the convenience of light in the day 

 time. The top surface of the roof and sliding shutter were 

 boarded over, and then covered with zinc, which was also 

 carried a few inches down the sides, rendering all perfectly 

 watertight. The sliding shutter referred to moves on rollers 

 between two strips of timber laid across the top of the build- 

 ing under the zinc, and is opened or closed by means of a 

 continuous cord, the ends of which are attached to the opposite 

 ends of the shutter and pass over appropriate pulleys, so that it 

 can be completely controlled without the necessity of going up 

 to it. The upright shutter is removed entirely when a front 

 view is required. 



It now merely remains to state that a facility for motion 

 was given to the roof by attaching an iron ring to the lower 

 elm circle. It was formed out of pieces of flat bar iron two 

 inches wide and about four feet long each, holes were drilled 

 through and counter sunk, and the bearing edge made straight, 

 the bars were then heated and bent to the required curve, they 

 were put on end to end, but not quite in contact, in order to 

 leave room for expansion, and very firmly screwed to the 

 circle. The roof was then lowered down, and when the 

 iron edging rested on the wheels, the whole fabric was 

 put in motion with a very slight effort. Tho movement 

 was rendered still easier by several convenient pushing handles 

 afterwards inserted, and a good supply of grease to ease the 

 friction. A few minor details remained to complete the 

 structure, such as painting inside and out, a bricked floor laid 

 upon a thick bed of ashes, a convenient shelf a foot wide 

 carried completely round the building above tho large elm 

 circle, from which depended a valance of oil baize intended to 

 hide the wheels and also to check the draft. The building has 

 now been in use for several months, and nobly stood the ordeal 



