THE SEICHES OF LOCH EARN. 



367 



bar. All that was necessary was to turn two shallow grooves in the rims of these 

 pulleys to keep the wire in position.* The recording waggon was arranged at such a 

 height that the wire could be clamped to it, exactly as the band is clamped in my own 

 model. The Sarasin thus modified worked perfectly, and is a very compact and fairly 

 portable instrument. 



Fig. 7 is a tracing of a limnogram furnished by this instrument running at 

 its high speed (2*977 mm. per minute). The scale is f. As the limnograph was 

 placed near the eastern binode, the trace is nearly sinusoidal ; but shows well-marked 

 embroidery, as the weather was not calm. 



The Statolimnograph. 



In studying the vibrations of Loch Earn, that is the denivellations, generally of 

 very small range, whose period of fluctuation is a minute or less, the want was felt of 

 a self-registering limnograph, as sensitive as our Endros index limnographs (which 



_J^W 



Fig. 8. 



multiply about four times), and having an equally open time-scale. This want was 

 supplied by utilising a Kichard statoscope, which had been put at our disposal by the 

 Lake Survey, originally for the purpose of studying sudden changes of the barometric 

 pressure in connection with seiches. 



The nature of the statoscope will be understood from fig. 8, where it stands on the 

 left. It consists essentially of a cylinder, S S, communicating with the outer air by a 

 stop-cock C. Into this cylinder is let a set of aneroid capsules of the usual construction, 

 except that they are not sealed up but open ; so that the interior communicates freely 

 with the outer air. A rod fixed to the bottom of the set of capsules is jointed to 

 the end of a system of multiplying levers, which work a recording pen, exactly as in 

 the ordinary barograph. The time-scale of the recording drum is about 5*3 mm. to 

 the minute. When the stop-cock C is open, the pressure inside and outside the 

 capsules is the same, and the pen remains at zero. When C is closed and the air in 

 the cylinder isolated, then, supposing the temperature inside to remain constant, the 

 displacement of the pen at any time is proportional to the difference between the 

 atmospheric pressure at that time and the atmospheric pressure at the time when C 



* If preferred, a steel band could be used, by turning the rims of the two pulleys flat. 



