SI 4 Professor Forbes' s Account of 



bottom ; the shaft fills very slowly, and the flow of water and 

 gas continue for a long time progressively to increase, not ap- 

 parently attaining their maximum until the water is at its full 

 height, which requires from thirty to forty minutes after the 

 first return of the stream. It remains in a state of violent agi- 

 tation for about two hours, or somewhat more, when the pre- 

 ceding cycle of phenomena is repeated. 



I must not omit to mention certain hollow sounds {dumffe 

 T67ie), about which much has been said and written, stated to 

 be audible both at the descent and flow of the water, resem- 

 bling the report of very distant artillery or drums. I have of- 

 ten listened for these without hearing them. I have, however, 

 once or twice perceived them when the gas began to be dis- 

 charged pretty briskly, and am disposed to attribute them to 

 concussions of the great column of water occasioned by partial 

 disengagements of gas. 



The extreme improbability of the unanimous report I re- 

 ceived, that the frequency of the intermission depended upori 

 the number of pumps at work, and that its regularity was in a 

 great measure destroyed if these were stopped altogether (as is 

 the case in winter), aitd the importance of such a fact upon the 

 theory of the phenomenon, led me to examine it with the 

 greatest attention : a register was kept by order of the autho- 

 rities, of the time of ebbing and flowing of the spring, com- 

 mencing on the 10th of July 1838. This was kept by the 

 persons officially stationed there, connected with the baths. I 

 arrived at Kissingen on the 22d, and examined this register al- 

 most daily afterwards until the 24th August, so as to confirm 

 its general accuracy. I believe that the observations were 

 never forged, and were generally within a few minutes of the 

 truth. The results of an attentive examination of it are the 

 following : — (1.) That even when the same number of pumps 

 worked, there is a considerable deviation from the average time 

 of ebb or flow, amounting occasionally to a fourth or fifth part. 

 Thus fifty-three observations of the time of flow, whilst five 

 pumps acted, give a mean duration of 2 hours 46 minutes ; but 

 in five instances it exceeded 3 hours 30 minutes, and in one in- 

 stance fell below two hours. (2.) The periods of flow seem 

 usually to have been greater in the afternoon than in the morn- 

 ing. (3.) When the number of pumps was suddenly and 



