30 ©. B. Comstock—Zine Bar Variation. 
PRELIMINARY REDUCTION. 
§7,-8’, Z’,—Z’, 
Date. he ta. residuals. residuals, 
1881. ; P # 
Mar. 14, 9.40 A. M. 39°74 F. 39°82 F. —1°0 —2°3 
‘ 15, 9.39 P. M. 40°58 40°67 —3'8 —5°2 
Stig. sar BOLe ae 41°79 41°80 8°9 —2°5 
AT, Oot AS 41°90 41°90 7 —2°4 
Tube 1 from Mar. 17, 9.30 a. M. to Mar, 18, 9.15 A. M., was kept at a tempera- 
ture between 70° and 80° F. 
Mar. 15," 8,15 Pou. 46°51 45°12 1041 _58°9 
oo) WO) O44 Al 44°25 43°69 — 84 46°8 
Le, eee P, We 44°02 43°52 + 0°9 —38°8 
19, 8.08 P. M. 43°88 43°50 + 2°% —42°1 
Dr (BOs) So Aa Me 43°66 43°37 + 46 —33°5 
og 8.30 P.M, 43°70 43°45 — 6°4 —38'8 
25, 10.235 A.M. 43°47 43°33 +) 3° —35°3 
aeiye EO, Me 43°51 43°32 + Ll 33°4 
Co 2a, ola A. Me 43°33 43°12 + 2°6 —28°8 
22, 8.43 P. M. 43°03 42°90 — 49 —26°4 
© 23,° SISA 42°76 42°59 — 0:6 —29'7 
An examination of the residuals shows that the mean 
residual of S’,—S’, before heating was —5"-8, and allowing 
forty-eight hours to cool, that the mean residual from 9" 39" 
A. M., March 20, to 9" 18™ A. M., March 23, was 0”-0, differing 
5-8 from the previous value, a quantity too small, in view 
of the very large residuals before heating, to indicate a change 
in S’,—S’,. But the mean residual of Z’,—Z’, before heating 
was —3'-1, and after heating, between March 20, a. M. and 
March 23, was —32"2, a change of 29". 
It seems, then, that the heating from 41° F. to 75° F., 
and subsequent cooling to to 43° F., increased the length of the 
four-meter zinc bar about 29", This would give a change 
of 7" per meter for a temperature change of 30°, or about half 
the ahnaiye found for the zine ml of the meter (M. T. 1876) for 
+75° 
a temperature change from —3° 
Sufficient data have ary yet bs obtained to determine the 
The question at one whether bars of other metals 
may have asinible differing pak at the same temperature. 
U. S. Lake Survey Office, Detroit, Mich., April 30, 1881. 
