Figure (5. — The result of earl) pendulum 

 experiments was often expressed in terms of ili<' 

 length ol .1 pendulum which would have a 

 period of One second and was < ailed "the seconds 

 pendulum." In 1792, J. C. Borda and J. I). 

 Cassini determined the length of the seconds 

 pendulum .h Paris with this apparatu 1 

 pendulum consists of a platinum ball about i 1 ; 

 Inches in diameter, suspended by a fine iron 



wire. Ill'- length, about [2 feet, was such thai 



its period would l«- nearl) twice as long as that 

 nt the pendulum "I the 1 It 1 k 1 \>. I he interval 

 between coincidences was determined l>\ ob- 

 serving, through the telescope at the left, the 

 times when the two pendulums emerge together 

 from In-hind the screen (M). The exact length 

 11I the pendulum was measured in a platinum 

 scale (nol Bhown) equipped with a verniei ami 

 an auxiliary copper scale foi temperature 

 c mice lie .11. 



When, ai the end of the 1 8th century, the 

 French revolutionary government established 

 tin- metric system of weights and measures, tin- 

 length of the seconds pendulum at Paris was 

 Considered, but not adopted, as the unit of 

 length. (Plate -•. Vfemoirei publiei pen Ui Societe 

 francedse de Physique, vol. 1 



° fc j M ' 



pendulum was use. I liv other observers ami finall) was 

 losl ai sea ' n an expeditit u around the world. The 

 knowledge oi the- pendulum acquired by the end of the 

 Kith century was summarized in 1783 in a memoir by 

 Bosco\ ich. 1 ' 



'• Pere R. J. Boscovich, Optra periinenlia ad Opiicam el 

 Astronomian (Bassani, I '85), voL ?. no. 3. 



rhe practice with the "simple" pendulum on the 

 part of Picard, Bougui . I a I and others 



in France culminated in the work of Borda and Cas- 

 sini in 1792 ai the observatory in Paris *° (fig. 6)- The 



: I J. D. Cassini de Thurv, "Exp£riences 



pour connaitre la longuer du pcndule qui bat les secondes a 



Collection de mhnoires, vol. 4, pp. 17-64. 



PAPER 44: DEVELOPMEN1 01 GRAVITY PENDULUMS IN THE 19TH CENTURY 



311 



