362 On the Ventilation of Lighthouse Lamps. [1843. 



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 ordinary 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 pre- 

 paration now described been also added, it is probable that the 

 time would have appeared astonishingly increased. 



I am, Gentlemen, yours, &c., 

 M. FARADAY. 



On the Ventilation of Lighthouse Lamps ; the points necessary 

 to be observed, and the manner in which these have been or 

 may be attained*. 



THE author states that the fuel used in lighthouses for the 

 production of light is almost universally oil, burnt in lamps of 

 the Argand or Fresnel construction ; and from the nature and 

 use of the buildings, it very often happens that a large quan- 

 tity of oil is burnt in a short time, in a small chamber exposed 

 to low temperature from without, the principal walls of the 

 chamber being only the glass through which the light shines ; 

 and that these chambers being in very exposed situations, it is 

 essential that the air within should not be subject to winds or 

 partial draughts, which might interfere with the steady burning 

 of the lamps. 



* Proceedings of the Institution of Civil Engineers, June 2/, 1843, p. 206. 



