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 arrangemeHt is jvained ironi Fig. 28. In Fig. 38, a a' is the 



Fig. 38. 



Plan of Observatory (upper floor). 



floor ot the gallery, h // //' the circuliir npertur(> in which tlu^ telescope c c' turns. 

 The staircase is indicated by (/. The Enlarger, § 6, rests on the shelf f, the helios- 

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

 tables, /■ the water tank, /• the tap and snd<, / the stove, m a heliostat shelf, // tlie 

 door, n the window. 



Th(> building is kept ventilated by opening the door in the lower ])art, anil the 

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

 mer day the ni)]>er parts, aiul esp(>cially those close under the dome, become without 

 this precaution \ery hot, and this occurred even before the tin roof Avas painted. 

 Bright tinplate seems not to be able to reflect by any means all th(> heat that falls 

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

 have lighted in a few moments dry up, and soon become i)ul\iri/al>le. A knowledije 

 of these facts led to the abandonment of wooden sheathing niub'r tlie tin, for without 

 it when night comes on the accumulated heat radiates away rai)i(ilv, and ceases to 

 cause aerial currents near the telesco])e. 



The interior of the l)nilding is i)ainted an<l wainscoted, and the roof is orna. 

 mented partly in hiui' and oak. and |)artly with ])auels of tulip-tree wood. 



'I'here are only twd windows, and tliey an; near the southern angles of the roof. 

 ^Vhile they admit sunshine on some occasions, they can on oflu-rs be closed, and 

 tlu^ interior l)e reduced to darkness. In the southeast corner a small openiu'' t 



