C. G. Rockwood—Motion of a Tower by Solar Heat. 188 
powers of absorption, radiation and conduction of the materials 
of the tower have been left entirely unnoticed. They would 
undoubtedly have their place in a complete investigation, but 
no data were at hand for estimating their influence. 
we may suppose the tower to be equally expanded in all 
parts of its height, the vertical side would be changed ¢ 
into a uniform curve, as AB in the figure; and since the | & 
deviation from a vertical is small, the tangent at 
would cut the vertical line BC nearly at the middle 
int between Band ©. Therefore CD is nearly one- 
major axis of the ayes should be proportionately diminished. 
Contraction of that side upon which it blew was thus plainly 
recorded hy the level, na a good illustration afforded of the 
duct of the observations. 
_ Brunswick, Me., July 11th, 1871. 
