Expansion and Contraction of Building Stone. 137 
To ascertain the exact lengths of these pieces at the different tem- 
peratures produced by exposure to the weather—these alone being 
important for our immediate object, and for the purposes of con- 
struction generally, the measurements were made by means of a 
white-pine rod, with copper elbows at the ends embracing the stones 
when applied to them, as represented in the sketch. 
AA is an elevation, or vertical section lengthwise, of the stone to 
be measured; BB the measuring rod, with elbows D and C of thin 
hammered copper, firmly secured to it. The end D was always 
adjusted to the same part of the stone, by sliding through a groove in 
the copper guide F cemented to the stone; the elbow C was adjust- 
ed in like manner by sliding through a groove in the piece E also at- 
tached to the stone. The elbow C has itself a groove through which 
the wedge W may slide horizontally, under the guide E, between 
the elbow C and the stone: this wedge being graduated as a diago- 
nal scale showed, by the distance which it entered, the difference 
between the length of the measuring rod and that of the stone. The 
e ion of the measuring rod being known, the length of the stone 
could be calculated in decimals of a constant unit, viz. the English 
standard inch. 
A groove was cut in the stone in which a Thermometer was pla- 
ced, at each measurement, and being covered, was suffered to lie 
some time, in order to ascertain the temperature of the stone. ‘The 
temperature of the measuring rod was assumed to be that of the 
open air to which it had been exposed. 
By Lardner and Kater’s Mechanics, we have as a mean between 
the results of Capt. Kater and Doct. Struve for the linear expansion 
of deal wood in terms of its length for one degree of Fahr. the de- 
cimal .00000255 ; and by the Edinburgh Encyclopedia, art. Expan- 
sion, we find the decimal .00000944 to express the same for ham- 
mered copper. From these data the actual length of the measuring 
rod was calculated for each experiment; knowing its length at 
Vou. XXII.—No. 1. 18 
