121 



though the light of gas flames, concentrated into a very brilliant fo- 

 cus by means of thick plano-convex lenses, produced a very sensible 

 heating power ; it does not in the slightest degree blacken the chlo- 

 ride of silver, nor does it influence the combination of chlorine with 

 hydrogen, which is a yet more susceptible test of the direct influence 

 of the solar rays ; on the other hand, the brilliant light occasioned 

 by the discharge of the voltaic apparatus, presently blackens the 

 chloride of silver ; and when a mixture of chlorine and hydrogen is 

 exposed to its influence, it causes the production of muriatic acid, 

 sometimes quietly and sometimes with explosion, in the manner of 

 the solar rays. The concentrated rays of lunar light neither possess 

 heating powers, nor do they appear to influence chemical combi- 

 nation. 



In conclusion the author, after adverting to the inefficiency of 

 Mr. Leslie's photometer, for measuring the intensity of artificial 

 light, suggests an instrument in which the effects are measured by 

 the expansion of the vapour of ether, renewable from a column of 

 that fluid. 



On the Elasticity of the Lungs. By James Carson, M.D. Commu- 

 nicated by Thomas Young, M.D. For. Sec. R.S. Read Nov. 25, 

 1819. \_Phil. Trans. 1820, p. 29.] 



In a treatise published some years ago on the motion of the blood, 

 the author contended that the influence of the elasticity of the 

 lungs upon that function had been overlooked by physiologists. The 

 object of the present communication is to ascertain the real force of 

 this elastic power, as it exists in the healthy living body. For this 

 purpose Dr. Carson connected with the trachea of several animals a 

 glass syphon, so placed as to admit of pressure being exerted upon 

 the lungs by a column of water contained in it ; an opening was 

 made into the cavity of the chest on both sides, and the height of 

 the column of water in the tube was considered as equivalent to the 

 pressure exerted upon it by the elastic power of the lungs of an ox : 

 the author thinks it clearly ascertained " that the spring of air com- 

 pressed by a column of water, of a foot and a half high, is not equal 

 to the rebounding spring of the lungs at the usual stage of their di- 

 latation." The only experiment, however, which gave, in the author's 

 opinion, conclusive results, was made upon a dog ; for in all the 

 others the gradual sinking of the water to its ordinary level in the 

 syphon indicated some wound in the lungs. In the present case 

 the height of the column of water supported in the tube was ten 

 inches. 



Dr. Carson concludes this paper with some observations on the 

 modes of effecting artificial respiration, and on the method of ascer- 

 taining the actual quantity of air existing in the lungs after com- 

 plete expiration. 



