A SILVERED GLASS TELESCOPE. 



43 



scope, which only requires a cylinder 13 feet in diameter and 13 feet high. A gene- 

 ral idea of the internal arrangement is gained from Fig. 28. In Fig. 38, a a' is the 



Fig. 38. 



Plan of Observatory (upper floor). 



floor of the gallery, h V h" the circular aperture in which the telescope c c' turns. 

 The staircase is indicated by d. The Enlarger, § 6, rests on the shelf e, the helios- 

 tat being outside at/. The door going into the photographic room is at g, h h' are 

 tables, % the water tank, Tc the tap and sink, I the stove, m a heliostat shelf, n the 

 door, o the window. 



The buUding is kept ventilated by opening the door in the lower part, and the 

 dome shutter, seen in Fig. 37, for some time before using the instrument. On a sum- 

 mer day the upper parts, and especially those close under the dome, become wit/iout 

 this precaution very hot, and this occurred even before the tin roof was painted. 

 Bright tinplate seems not to be able to reflect by any means all the heat that faUs 

 upon it, but will become so warm in July that rosin Avill melt on it, and insects which 

 have lighted in a few moments dry up, and soon become pulverizable. A knowledge 

 of these facts led tcrthe abandonment of wooden sheathing under the tin, for without 

 it when night comes on the accumulated heat radiates away rapidly, and ceases to 

 cause aerial currents near the telescope. 



The interior of the building is painted and wainscoted, and the roof is orna- 

 mented partly in blue and oak, and partly with panels of tulip-tree wood. 



There are only two windows, and they are near the southern angles of the roof. 

 AVhile they admit sunshine on some occasions, they can on others be closed, and 

 the interior be reduced to darkness. In the southeast corner a small opening e 



