874 Traxsactions of tee American Institute. 



phere, or about fifty-two pounds per square inch in all, equal to a 

 depth of eigbty-five feet below the water. After entering the air- 

 lock, it wjus closed against the atmosphere, and the pressure equalized 

 •with that in the column, in the manner that has been already 

 described; and this operation, and the other one of equalizing with 

 the atmosphere when passing out of the column, were the only 

 times when difficulty from the air pressure was experienced. Men 

 of certain kinds of constitution sometimes sufiercd greatly, the 

 blood starting from the nose, ears and mouth, and the pain of 

 changing pressure being almost insupportable upon the eyeljalls 

 and drum of the ear. These were usually of a very nervous tem- 

 perament, and excitement would induce them to keep their nerves 

 under great strain, which added to their difficulties. No trouble 

 was experienced in procuring men, howev^er, w^ho could bear the 

 pressure perfectly well without injury. A little practice and 

 familiarity soon accustomed them to the circumstances. The mus- 

 cular action of SAvallowing would always relieve the ear drum 

 temporarily from pain and pressure, but after a little practice this 

 was found to be seldom necessary. With new men, the pressure 

 would be let on gradually; but those more accustomed to it, did 

 not hesitate to equalize as fast as their means of doing so allowed, 

 or in a space of less than a minute. 



The pressure once fully on, it would be difficult, from any bodily 

 sensations, to determine a difference of pressure amounting to at 

 least one atmosphere. The effect, while under air pressure, is to 

 cause a feeling of exhilaration, so sensil)ly felt by the workmen, 

 that a lazy man becomes industrious, and there is seldom occasion 

 to urge any of them in their work. The ventilation is of course 

 excellent, and the operation of breathing becomes so easy that the 

 inhalations are slower and longer than in the usual atmosphere. 



Upon leaving the column and again entering the ordinary atmos- 

 phere, the absence of the stimulus of so much oxygen produces a 

 certain degree of lassitude for a time, unaccompanied, however, 

 with any other difficulty. It could not be observed, either in our 

 case, or that of the workmen, that in an experience extending over 

 a period of nearly a year, any effect prejudicial to the health or 

 constitution w^as produced. 



It may be here stated that the men worked the same number of 

 -lours inside the columns as those outside, and that they were paid 

 but a slight advance over the wages of ordinary workmen. 



Where no obstructions ai-e met with, and the excavation ia 



