241? On holding the Breath for a lengthened Period. 



a clearer notion from the following experiment. Fill a pint or 

 quart jar with water over the pneumatic trough, and with a 

 piece of tube and a forced expiration throw the air from the 

 lungs in their ordinary state into the jar; it will be found that 

 a lighted taper put into that air will be immediately extin- 

 guished. 



A very curious fact connected with the time of holding the 

 breath was observed by Mr. Brunei, jun., and has, I think, 

 never been published. After the river had broken into the 

 tunnel at Rotherhithe, Mr. Brunei descended with a com- 

 panion (Mr. Gravatt, I think,) in a diving-bell, to examine the 

 place: at the depth of about 30 feet of water, the bell touched 

 the bottom of the river, and was over the hole ; covering it, 

 but too large to pass into it. Mr. Brunei, after attaching a 

 rope to himself, inspired deeply, and sunk, or was lowered 

 through the water, in the hole, that he might feel the frames 

 with his feet, and gain further knowledge, if possible, of the 

 nature of the leak. He remained so long beneath without 

 giving any signal, that his companion, alarmed, drew him up 

 before he desired ; and then it was found that either of them 

 could remain about twice as long under water, going into it 

 from the diving-bell at that depth, as they could under ordi- 

 nary circumstances. 



This was supposed to be accounted for, at the time, by the 

 circumstance that at the depth of 30 feet the atmosphere was 

 of double pressure, and that the lungs, therefore, held twice 

 as much air as they could do under common circumstances. 

 It is, however, quite evident that another advantageous cir- 

 cumstance must have occurred, and that the air in the lungs 

 was also better in quality than it would have been at the sur- 

 face of the river, as well as denser ; for supposing the deterio- 

 ration by breathing to continue the same for the same time, it 

 is clear that every inspiration passed into the lungs twice as 

 much pure air as would have entered under common circum- 

 stances : the injured air must, therefore, have been removed 

 more rapidly, and the quality of that at any one time in the 

 lungs must have risen in consequence. When to this is added 

 the effect of double quantity, it fully accounts for the increased 

 time of holding the breath ; and had the effect of the mode of 

 preparation now described been also added, it is probable that 

 the time would have appeared astonishingly increased. 



I am, Gentlemen, yours, &c. 



M. Faraday. 



