1886.] Mr H. Darwin, On a Self-recording Barometer. 



379 



cock not shown in the figure. The stop-cock is regulated so as to 

 allow a very small quantity of gas to pass. The pipe branches, 



and the gas can either pass into the indiarubber bag B or else 

 along the tube C. If this tube is closed, the gas will enter and 

 expand the bag and compel the board D to turn about the hinges 

 E. The pressure of the gas is more than sufficient to counter- 

 balance the weight at F ; consequently a certain amount of work 

 can be done during the upward movement; this gives the requisite 

 power to move the pen P. If more gas could pass along the tube 



