378 Mr H. Darwin, On a Self-recording Barometer. [Mar. 15, 



placed in the larger vessels containing the carbamate &c v and the 

 operation conducted in the usual manner. 



After 3 minutes A gave 10 c.c. Nitrogen 



The action is therefore much more rapid in the first instance 

 with the greater mass of bromide, but as the action proceeds the 

 weaker solution gains on it, and eventually all yield the same final 

 result. 



It appears therefore that this action of bromides belongs to the 

 type of certain so-called Catalytic actions in which the 'activity' of 

 the agent is explained by an intermediate stage of little stability. 

 We have in this instance perhaps stronger evidence of such a stage 

 than is often the case in many actions which are similarly ex- 

 plained. 



(3) On a Self-recording Barometer. By Horace Darwin, M.A. 



In all self-recording apparatus there must be some means 

 always at hand ready to perform the work required to keep the 

 record. In the case of a barometer a clock is used in conjunction 

 with some other motive power ; this may be the electric current 

 from a battery ; the radiation from a lamp acting on photographic 

 paper ; or the work obtained from the change of the atmospheric 

 pressure itself. The chief interest in the instrument shown in the 

 figure is the unusual source of energy employed ; the pressure of 

 the ordinary gas supply being made to do the necessary work. 

 This is undoubtedly an extravagant motor, but in cases like the 

 one before us the work required to move the mechanism is 

 extremely small, and the cost of the gas used is quite insignificant. 

 The ease with which the energy can be applied and the handiness 

 of the source makes this method most useful for a great number 

 of cases where governing and automatic regulating mechanism is 

 required. 



The gas from the main passes into the pipe A through a stop- 



