At the far end of the ice chamber, the whole of the ice had not been removed a 

 solid block of ice being left, 75 cm. high by 73 cm. broad and 160 cms. wide, with only 

 the upper part removed. This served as a very efficient and rigid pedestal for the 

 support of the pendulum stand, and worked very satisfactorily. (Plate 1.) 



To support the pendulum stand on the ice surface without danger of a change 

 of level, due to sinking in of the small base plates provided under the levelling screws, 

 these base plates were replaced by solid iron ones 4 inches square. This was found 

 quite sufficient to prevent any noticeable >sinking of the instrument. The iron base 

 plates were firmly cemented in place by warming them, allowing them to nielt a 

 little of the ice and then become frozen tightly in place. 



As stand for the coincidence apparatus two wooden cases were used one above 

 the other, firmly cemented to the ground and to one another by a mixture of snow 

 and water. A small oil lamp was at first used as a source of illumination for the flashes, 

 but was later replaced by a small electric lamp run from a set of dry batteries placed in 

 a box padded with seaweed. This prevented the freezing of the cells during the time 

 of observation. 



At first, an attempt was made to run the break circuit clock " S.C." in the cave 

 itself, but it was found impossible to keep it going for more than a few hours after 

 setting up. At the end of that period, the works became cold and the clock ceased 

 to go. This was due to the great viscosity of the oil at the low temperature prevailing 

 in the cave, and though it might have been obviated by the use of extra driving weights, 

 it was not thought advisable to do this.* 



The clock was finally hung on the wall of the main hut close to the box chro- 

 nometers, and the " time " was transmitted to the cave by the help of another observer 

 and by the use of portable telephone sets supplied by the National Telephone Co. 

 (Plates 2 and 3.) 



This was found to work fairly satisfactorily as, by a suitable arrangement of the 

 connections, it was possible for the observer calling the time from the clock in the hut 

 to hear the beats made by the action of the coincidence apparatus ; and these, of course, 

 were also heard by the observer in the cave. The proper numbering of the clock beats 

 was therefore fairly easily assured, though mistakes of one second or of ten seconds 

 quite frequently occurred owing to frosting up of the telephone by the observer's 

 breath. 



Four wires were required to make the necessary electrical connection with 

 the pendulum cave two for the telephone and two for the coincidence apparatus. 

 Accumulators formed the source of supply of the current. 



One of the most serious of the difficulties connected with work in the pendulum 

 cave was due to the lowness of the temperature. During the observations, the tempera- 

 ture of the ice walls of the cave varied from 20 to 30 C. ; and, owing to the small 



* It is essential that all chronometers, olorks, thermographs, etc., intended for use at very low 

 temperatures should be as free as possible from any oil. 



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