ASTRONOMICAL AND GEODETIC OBSERVATIONS. 69 



examination was made of the perpendicularity of the knife-edges to the longitudinal 

 axis of the pendulum, also of their plane which should pass through the same axis 

 — the test was found satisfactory. On this part of the theory of the physical pen- 

 dulum, the paper " On the Pendulum," by J. W. Lubbock, Phil. Trans. Roy. Soc, 

 1830, Part 1, p. 201, may be consulted. There is reason to suppose that the sup- 

 port of the pendulum case at the stations was sufficiently massive to guard against 

 induced vibrations. A fine mark on the supporting plate seems to have been used 

 to secure an identical contact with the knife-edges ; there are also two guiding pins 

 to indicate the central position of the bar between the plates. The plates show no 

 wear, and the knife-edges appear in perfect condition. 



It is very desirable that the Hayes' pendulum be swung at a number of other 

 stations' for the purpose of combining the results, and if possible to connect them 

 witli the accumulated series given by Baily. The connection could be made by 

 swinging the pendulum at Captain Sabine's station ot 1822-23 in New York City 

 (or as near to it as possible, since the old site of the Columbia College is now 

 inaccessible to such operations. Localities like Washington, D. C, and Key West, 

 Florida, would be well suited for new observations, and if combined with any made 

 at NeAV York would furnish a valuable contribution to our present knowledge of 

 the earth's compression as resulting from experiments of .vibrations. 



• As pendulum observations have a direct beai-ing upon the larger geodetic operations for ascer- 

 taining the earth's figure, and have recently again been considered for introduction in the Russian 

 and Indian arcs, I have taken occasion to bring the desirability of swinging the pendulum at some 

 stations of the United States Coast Survey, to the favorable consideration of the Superintendent. 



