TO KN( )\\ THE STARRY HEAVENS 



34i 



ture, was no light one. It was lifted 

 from the grinding table by a device 

 such that the stress would be evenly 

 distributed throughout the disc. Then 

 it was lowered into an octagonal box 

 which had been lined with paraffin pa- 

 per and was sealed at every joint to 

 exclude the dust. Inside the paper was 

 a packing of carded wool and Brussels 

 carpet to protect from heat and jolting. 



100 feet high, constructed of metal and 

 has double walls, so that the tempera- 

 ture can be kept as even as possible. 

 The lower 28 feet is stationary and the 

 upper part rotates. Forty huge piers 

 surrounding a still larger central pier 

 supply the foundation. The main pier 

 rests on a bed of sand six feet deep and 

 carries a circular floor 52 feet in diam- 

 eter. This has around its outer rim a 



THE DOME FOR THE 100-INCH REFLECTOR OF THE MOUNT WILSON SOLAR OBSERVATORY. 



Only the very edge of the silvered sur- 

 face touched anything. A correspond- 

 ing rim of wood, faced with carpet and 

 wool, had been placed inside the box 

 cover and held the mirror rigidly in 

 place when the cover was screwed 

 down. The box was then hermetically 

 sealed and encased in another layer of 

 paraffin paper and clamped between 

 parallel sets of heavy timbers with a 

 steel bolt at the top for lifting. Even 

 this did not seem enough and a cradle 

 of heavy timbers was bolted on the 

 bed of the motor and this was lined 

 with cushions in which were heavy 

 springs so that the box might oscillate 

 easily. A strong canvas covered this 

 and the trip was successfully made to 

 the top of the mountain in one day. 



Scarcely less interesting than the 

 mirror itself is the mounting. The 

 larger parts of this were constructed 

 in a shipyard for battleships and the 

 work was delayed very much by the 

 increased activity in ship construction 

 after the beginning of the war. The 

 dome which shelters the telescope is 



metal wall nine feet high, to keep 

 drafts from penetrating to the upper 

 part of the dome. The moving parts 

 of the telescope weigh 100 tons and 

 the bulk of this weight is borne by 

 pedestals floating in Mercury, 



The driving clock has a weight of 

 one and one-half tons and winds auto- 

 matically every ten minutes. There is 

 an elaborate system of electric con- 

 trols, so that the observer can move 

 the telescope any distance in any direc- 

 tion he chooses, rotate the dome and 

 move the platform without leaving his 

 chair. 



The telescope is fitted with a fine 

 spectrograph and much of the work 

 will probably be done with this instru- 

 ment. Undubtedly a large amount of 

 work will be done in gathering data for 

 Kapteyn's work on star-streams and to 

 add to our knowledge of the structure 

 and limits of the universe. The huge 

 increase of light-gathering power 

 should help materially in the study of 

 star clusters and nebulae. 



