ie, hee eda a th te) Si rl *, 
of bars at the temperaturefof melting ice. 449 
3d. Gide aine bar, which is 1°03" long and 27™™ square in 
cross-section. It was cast in the summer of 1881. The ordi- 
hary zine of commerce was used, and the bar was cast in a 
vertical position. About 0-2" of the upper end of the casting 
was cut off. The top half of the bar at each end is cut away 
for a distance of 2™, so that the graduations cross the neutral 
axis. This bar was also oraanedl and its length and expan- 
sion were determined by Professor Rogers. It is designated Z,. 
4th. Two glass meters. They are of French plate, 1-02" 
long, 8™ thick and 51™ deep. Half the depth of either bar 
at each end is cut away for a distance of 2™, and the gradua- 
tions cross the neutral axis. They are designated G, and G, 
respectively. 
: . One copper meter. It was cast in February, 1883, and 
18 1°02™ long, 20™ wide and 22™™ deep. Its graduations cross 
the neutral axis. It is designated C,. : 
6th. One brass meter. It was cast in February, 1883, and is 
composed of ten parts of copper to three of zinc. It is of the 
Same form and dimensions as the copper meter. It is desig- 
hated B.. 
Comparisons are made in the following manner: 
The bars to be compared are each placed in a wooden box 
1-1™ long, 0-1" wide and 0-1™ deep. The bars are supported 
in their boxes at two points distant about one-fourth and three- 
fourths the length of the bar from either end. Tbe boxes are 
filled with finely powdered ice so as to completely surround 
the bars except at small spaces near the graduations. The 
boxes are placed on a shelf under the microscopes. Each box 
has three leveling screws which rest on plates of glass, so that 
the bars may be easily adjusted to any requisite position. The 
Am. Jour. Sc1.—Tuiep Series, VoL. XXV, No. 150.—Junx, 1883, 
30 
