Peirce added that it seemed to him that if the revers- 

 ible pendulum perhaps is not the best instrument to 

 determine absolute gravity, it is, on condition that 

 it be truly invariable, the best to determine relative 

 gravity. Peirce further stated that he would wish 

 that the pendulum be formed of a tube of drawn brass 

 with heavy plugs of brass equally drawn. The cylin- 

 der would be terminated by two hemispheres; the 

 knives would be attached to tongues fixed near the 

 ends of the cylinder. 



During the years 1881 and 1882, four invariable, 

 reversible pendulums were made after the design of 

 Peirce at the office of the U.S. Coast and Geodetic 

 Survey in Washington, D.C. The report of the super- 

 intendent for the year 1880-1881 states: 



A new pattern of the reversible pendulum has been in- 

 vented, having its surface as nearly as convenient in the 

 form of an elongated ellipsoid. Three of these instru- 

 ments have been constructed, two having a distance of 

 one meter between the knife edges and the third a dis- 

 tance of one yard. It is proposed to swing one of the 

 meter pendulums at a temperature near 32 ° F. at the 

 same time that the yard is swung at 6o° F., in order to 

 determine anew the relation between the yard and the 

 meter." " 4 



The report for 1881-1882 mentions four of these 

 Peirce pendulums. 



A description of the Peirce invariable, reversible 

 pendulums was given by Assistant E. D. Preston in 

 "Determinations of Gravity and the Magnetic Ele- 

 ments in Connection with the United States Scien- 

 tific Expedition to the West Coast of Africa, 1889- 

 90." 75 The invariable, reversible pendulum, Peirce 

 no. 4, now preserved in the Smithsonian Institution's 

 Museum of History and Technology (fig. 34), may be 

 taken as typical of the meter pendulums: In the same 

 memoir, Preston gives the diameter of the tube as 

 63.7 mm., thickness of tube 1.5 mm., weight 10.680 

 kilograms, and distance between the knives 1.000 

 meter. 



The combination of invariability and reversibility 

 in the Peirce pendulums was an innovation for rela- 

 tive determinations. Indeed, the combination was 

 criticized by Maj. J. Herschel, R.E., of the Indian 

 Survey, at a conference on gravity held in Washington 

 in May 1882 on the occasion of his visit to the United 



"' Report of the Superintendent of the U.S. Coast and Geodetic 

 Survey for 1880-81 (Washington, 1883), p. 26. 



78 Report of the Superintendent of the U.S. Coast and Geodetic 

 9 90 ^Washington, 1891), app. no. 12. 



Figure 20. — Support for the Peirce pendulum, 

 1889. Much of the work of C. S. Peirce was con- 

 cerned with the determination of the error introduced 

 into observations made with the portable apparatus 

 by the vibration of the stand with the pendulum. 

 He showed that the popular Bessel-Repsold appara- 

 tus was subject to such an error. His own pendu- 

 lums were swung from a simple but rugged wooden 

 frame to which a hardened steel bearing was fixed. 



States for the purpose of connecting English and 

 American stations by relative determinations with 

 three Kater invariable pendulums. These three 

 pendulums have been designated as nos. 4. 6 (1821), 

 and ll. 76 



Another novel characteristic of the Peirce pendulums 

 was the mainly cylindrical form. Prof. George 

 Gabriel Stokes, in a paper "On the Effect of the 



76 Report of the Superintendent of the U.S. Coast and Geodetic 

 Survey for 1881-82 (Washington, 1883). 



328 



l'l I I (TIN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



