58 0. E. SCHI0TZ. [NORW. POL. EXP. 



June is as much as 145 units in the seventh decimal-place less than that 

 found on the 10th, although the two points of observation lay no more than 

 about 5 km. apart, above a depth of over 3000 metres. If we especially exa- 

 mine the period for pendulum 34, with which experiments on the 8th, 

 10th and llth June were made, we find that the period decreases regularly 

 from the 8th when, as we shall subsequently see, it was about normal to 

 the llth. We must suppose that after the violent wind of the 9th June, 

 internal tremblings have commenced in the ice-masses, and have increased in 

 strength on the 10th and llth, as the force of the wind diminished, and the 

 rate of the drift became slower. I think we may conclude that this has really 

 been the case, from the fact that Lieut. Scott-Hansen, on the llth, expressly 

 mentions that he heard rumblings in the ice during the first comparison of 

 clocks, previous to the commencement of the pendulum observations. These 

 observations are thus easily explained by the influence - - already pointed 

 out by me - of imperceptible tremblings upon a pendulum's period of 

 oscillation. 



As the observations show, the pendulums have only altered in a very 

 slight degree during the expedition. The mean period of oscillation before 

 the departure of the expedition was 0'5060400 in the Observatory, and after 

 its return, 0'5060389 in the new pendulum-house in the Observatory Garden. 

 The difference only amounts to 11 units in the last decimal-place, and 4 or 

 5 of these may be attributed to the difference in elevation 5'6 m. between 

 the two points of observation 1 , thus leaving a difference of only 7 units 

 due to an alteration of the pendulums during the expedition. This alteration 

 is so small that the pendulums may safely be considered as unchanged during 

 the expedition, with a mean period of oscillation in the Observatory equal to 

 0'5060397, corresponding to the mean of the period of oscillation in the same 

 place before and after the journey. 



If we start with the value found by VON OPPOLZER for the acceleration 

 of gravity in Vienna (Turkenschanze), viz. 



g = 9-80866 m., 



1 When the new pendulum-house was taken into use, an attempt was made to deter- 

 mine directly the difference between the periods at the two places. No certain diffe- 

 rence was obtained. 



