Thos. Mudd — Analogy of Earthquake Phenomena. 177 



VIIL — Suggested Analogy bktween "Water Hammer" Action 

 AND Earthquake and Volcanic Phenomena. 

 By Thomas Mudd. 



PROF. PEESTWICH, in his paper in the January Number of this 

 Magazine on the " Causes of Volcanic Action," assumes the 

 existence of hot reservoii's or cavities filled with molten rock, and 

 cold reservoirs or cavities, nearer the surface, filled with water ; and 

 he supposes the shrinkage of the Earth to squeeze up the molten 

 rock till it meets with the water, which then explodes, producing a 

 volcano. 



I would suggest that the action which goes on in the fissures that 

 connect the hot and cold cavities is similar to the " water hammer" 

 action, so well known to engineers. This assumption is necessary, 

 it seems to me, to render the theory completely satisfactory. 



Water hammer action manifests itself where steam has to be con- 

 veyed to considerable distances from its source without any return 

 communication or easy vent. It occurs in this way. The steam, on 

 being turned into the cold pipes, is quickly condensed, and in a short 

 time a quantity of water is formed. The steam condensing most 

 quickly at the end furthest from the inlet, there is there formed a 

 partial vacuum. The steam rushing forward in consequence, gathers 

 up the water into a plug, which fills the sectional area of the pipe, 

 and forms indeed a water piston. This water piston is dashed by 

 the force of the steam against the end of the pipe, producing a 

 severe shock, accompanied by a loud report ; and then follows 

 by natural sequence a I'ebound, which must be a rebound of a com- 

 pound character, made up in part of the rebound of the steam, in 

 part of the rebound of the water, and in part of the effort of the 

 water to regain its level b}' gravity. The first two are probably of 

 momentary existence, but the last takes time, and proceeds with a 

 measured swing like a mighty pendulum. When the force of the 

 return wave is spent, and the steam again gets the advantage, con- 

 densation having in the mean time been going on behind the return 

 wave, this piston of water advances a second time, and is dashed 

 with increased fury against the obstruction in the pipe. This action 

 in a few strokes arrives at its maximum, and thence, if the pipe has 

 been able to withstand the shocks, gradually diminishes and dies 

 away. 



There are two operations at work affecting its destiny. Tlie 

 quantity of water set in motion is increasing, tending to increase the 

 shock, and the temperature of the pipe is heightening, tending to 

 diminish the shock by reducing the difference of pressure between 

 the spaces before and behind the water plug. The latter is by far 

 the more potent agent, and quickly rediices the water hammer action 

 to nothing. 



Now the essentials to this kind of action are — 1. A length of 

 passage confined at its extremity. 2. A fluid. 3. A condensible 

 vapour. 4. A difference of temperature at the two extremities of 

 the passage. 5. The initial action, which is merely the introduction 



decade II. — VOL. IX. NO. IV. 12 



