368 PROFESSOR CHRYSTAL AND MR JAMES MURRAY 



was closed. In the advertisement of the instrument it is said that for a difference of 

 1 mm. of mercury the pen shows a displacement of 25 mm. In our instrument this 

 displacement was nearer 20 mm. ; but this may have been due to a repair which was 

 necessary after the return of the Antarctica, on board of which the instrument had been 

 used for observations on ocean waves. In order to minimise the variation of tempera- 

 ture, the cylinder S S is packed with non-conducting material. Nevertheless, the 

 temperature does vary slowly ; and this must be attended to in using the instrument. 



The statoscope is converted into a statolimnograph by the arrangement shown in 

 fig. 8. W is a closed well with tubes fitted at the top and bottom. To the bottom 

 tube is attached an india-rubber access tube similar to that used with an ordinary index 

 limnograph. The tube at the top of the well is fitted with a screw vent-plug, by means 

 of which the pressure inside W can be made equal to the atmospheric pressure at will. 

 By means of a branch from the top tube, and a connecting tube C C, the well is put in 

 communication with the cylinder of the statoscope, the stop-cock C being, of course, 

 open. 



When a limnogram is to be taken, the well is placed on a board with a hole in it 

 to let the lower tube pass through. This board is supported on stones, so that the 

 access tube, A A, passes freely under it, and the water stands about half-way up the 

 inside of the well, the vent-plug being, of course, open, and the level outside and inside 

 W the same. The vent-plug is then closed ; and the rise and fall of the lake level causes 

 a corresponding rise and fall inside W, which compresses or rarities the confined air, 

 thus causing proportional differences of pressure between the outside and inside of the 

 capsules. These differences are registered by the recording pen, and thus we get a 

 limnogram. When the apparatus is working as a limnograph it is not affected by small 

 variations of the barometric pressure — as these take effect equally within the capsules 

 and at the lake level, from which they are transmitted through the well to the inside 

 of the cylinder, i.e. to the outside of the capsules. A considerable change of the 

 barometric pressure during an observation would, of course, alter the mean level in 

 the well and thus affect the mean volume of the confined air, which would slightly 

 alter the sensitiveness of the instrument. It is obvious that the larger the diameter 

 of the well and the smaller the volume of confined air (in W, C C, and S S), the greater 

 will be the change of internal pressure for a given rise of the lake level. We shall 

 consider the theory more in detail later on. 



The statolimnograph was found to work admirably, and gave traces of great 

 variety and interest. A few specimens are given in figs. 9-12 ; the significance of the 

 results obtained will be explained in a later communication. 



The arrangement of the apparatus in actual use is seen in fig. 13, where it is seen 

 between the observer and the boat, partly on shore and partly in the lake. 



Alternate. Use of the Statoscope as a Limnograph and Barograph. — In order to 

 convert the arrangement above described into a very sensitive barograph, we have 

 merely to shut the stop-cock C. The instrument then proceeds to register the 



