Movement of the dome of the Capitol at Washington. 385 
The distinguished architect, Mr. Thomas M. Walter, sup- 
posed naturally enough, that this enormous amount of iron 
would be more or less affected by the action of the sun’s rays— 
causing an expansion, to meet which he had been making, 
throughout his protracted labors, all possible provision. To 
ascertain what this effect would be, he suspended a wire from the 
center of the ceiling of the Tholus, or crowning cupola, under the 
feet of the statue. At the extremity of this wire nearest the 
ground, or pavement of the rotunda, he arranged a delicate 
mechanism, that carried a pencil, whose point rested on a sheet 
__ Of paper, on which it was expected that expansion and contrac- 
_ tion would record their effects. It was Mr. Walter's expectation, 
probably, that, as the sun moved from the east to the west, some- 
thing of a uniform curve would be traced by the pencil’s poms 
upon the paper, furnishing, in that way, data that might be as 
useful as they would be origi 
ginal. 
iu ‘ eee a 
this on Zaps 
ees > § : \ ¥ 
LA 
f—~ DECI TPM mn 
2 
DEC. 12. 1864°-7.P.M 
the wind, and not the sun made 
: tions, and recorded its 
h the agency of the vast mass of the dome. One would 
win 
eg a hat a day was capa- 
e diagram above shows wh ey eee: i 
red; and when, too, 
reered round the points of the com That chim- 
