THE HEART OF THE ANTARCTIC 



The recording part of the instrument was a modified 

 barograph. A box weighted with stones was put down 

 through a hole in the ice as an anchor. iThe wire from 

 this anchor was taken over a pulley hung from a tripod 

 of bamboo poles. It was then attached to one end of a 

 long lever of bamboo, which was weighed to keep the 

 wire taut. By the arrangement of the lever the record 

 of the tide movement was reduced to one twentieth and 

 thus brought within the limits of the barograph drum. 

 The parts above the ice are shown in the photograph. 

 The wire in passing through the ice is enclosed in a tube 

 which is kept filled with oil, as used for the same purpose 

 on the Discovery expedition. The instrument worked 

 well, and a continuous record was got for about three 

 months interrupted only for half an hour weekly, when 

 the papers were changed. At the end of that time the 

 wire broke from the box at the bottom of the sea, and the 

 tripod was blown down during a severe blizzard. The ice 

 was then so thick that it was found impossible to cut a 

 hole to put down another anchor. 



The tide -record obtained on the barograph drum was 

 a simple undulating curve with one maximum per day, 

 attaining the greatest amplitude at full and new moon, 

 and diminishing almost to nothing at the quarters, when 

 shorter waves of less amplitude could be seen. 



When the record was analysed it was resolved into two 

 undulations, the larger one having the period equal to the 

 lunar day, the smaller one having a period of half a day. 

 As one maximum per day of the lesser tide coincides with 

 the maximum of the greater tide, its effect on the original 

 record is to increase the apparent amplitude in that 

 phase, while the other maximum of the lesser tide causes 

 a flattening in the opposite phase of the greater one. 



This figure shows the results of an analysis of the 

 same portion of tide-record shown in the previous figure. 



396 



