The period of all three observing pendulums remained almost unaltered during 

 the period between the first and last observations at Potsdam, and this may in part 

 be ascribed to the fact that they were already thoroughly " seasoned " by their previous 

 work. Their record goes back to the journeys undertaken by Dr. 0. Hecker in 1902 

 and in 1904-5, for the determination of the value of gravity over the Atlantic, Pacific, 

 and Indian Oceans. They were again used by Professor Haasemann in 1906 in carrying 

 out the programme of the Potsdam Geodetic Institute. 



A 

 B 



Fig. 1. Diagram showing construction of half-second pendulums. 



In the series of observations here described, they acted as satisfactorily as could 

 be expected of pendulums with such a high temperature coefficient as brass, though no 

 doubt it would have been a very great advantage to have possessed pendulums made 

 of invar, or even of quartz. 



The chief cause for regret is that the gilding of No. 21 suffered somewhat during 

 the course of the first winter's observations at Cape Evans. The, reason for this may 

 be the adhesion of particles of the drying agent kept within the case of the instrument 

 in order to prevent the accumulation of hoar-frost on the mirrors. That this action 

 has affected the period of the pendulum so little is strong evidence in support 

 of Professor Haasemaun's contention that the main factor in preserving the period 

 unchanged is connected with the " set " of the agate knife-edge, rather than with a 

 lack of alteration on the surface or within the mass of the pendulum. 



3 A 2 



