82 A. M. Mayer—Effects of Magnetization 
the apparatus which has greatly aided in giving to the geodetic 
work of our National Coast Survey its renowned precision, and 
in rendering accurate the comparisons and constructions of our 
office of Weights and Measures. A detailed description, with 
drawings, of this instrument will be found in the “ Report on 
the Construction and Distribution of Weights and Measures, 
Washington, D. C., 1857,” written by Dr. A. D. Bache, the late 
President of the Academy.* 
The Measuring Instrument. 
I will now describe the actual adaptation of this instrument 
to our research. The drawings 1 and 2 give respectively an 
A 
jw 
—<$— a9 4 
brass caps of the rods experimented on. ‘These rods were 
60-1 inches long, ‘5 inch in diameter ; and each rod weighed, 00 
the average, 1520 grams. While the ends of a rod rested 10 
springs, ss, which took hold of the rod at distances from its 
ends equal to $ of its length. The flexure of the rod was thus 
in great part avoided, and it could therefore be accurately cen- 
against its agate terminal. This operation was performed 4s 
* To my friend and colleague, Dr. J. E. Hilgard, of the U.S. Coast Survey office, 
I am indebted for the loan of the comparator used in these researches. 
