268 



of pneumatic chemistry, he is led to the conclusion, that the arrange- 

 ment of each of the gases in the united column will be precisely the 

 same as if the other had no existence ; that is, that each will form a 

 separate and independent atmospheric column, containing at its base 

 a pressure of fifteen inches, and decreasing in density according to 

 its own peculiar law ; so that after a certain height the limit of the 

 carbonic acid atmosphere being passed, hydrogen alone would exist 

 in the column, and after the limit of the hydrogen atmosphere were 

 attained a vacuum. 



The author takes occasion, in the course of this reasoning, to sug- 

 gest, that the absolute height of an atmosphere of carbonic acid or 

 other gas might be found by perfectly exhausting a tall receiver, 

 then letting in a small given portion of the gas, and testing the upper 

 and lower portions, to ascertain its presence below and absence above. 



He terminates the paper, 1st, by a view of the constitution of the 

 earth's atmosphere on this idea ; according to which it appears, that 

 the atmosphere of oxygen being supposed to reach to the height of 

 38 miles, that of azote will reach to the height of 54 or 44, according 

 to the different assumptions which may be adopted respecting the 

 weight of its atom ; that of carbonic acid to 10 miles, and that of 

 aqueous vapour to 50 miles : and 2ndly, by a comparison of this view 

 with what should be its constitution on the usual theory : the whole 

 of this view of course supposes the air to be perfectly at rest, but the 

 actual constitution of the atmosphere is probably materially modified 

 by the motions perpetually going on in it. 



On the Coagulation by Heat of the fluid Blood in an aneurismal Tu- 

 mour. By Sir Everard Home, Bart. V.P.R.S. Communicated 

 January 23, 1826. Read March 2, 1826. [Phil. Trans. 1826, 

 Part III. p. 189.] 



In a case of aneurism of the external iliac artery, the author tied 

 the femoral artery below the sac ; but as this neither diminished the 

 pulsation nor arrested the increase of the tumour, he was led to in- 

 troduce a needle into its centre, connected with a heated bar of steel : 

 as no severe pain was thus produced it was retained for fifteen mi- 

 nutes, during which the pulsation was diminished. On the twentieth 

 day after the operation, the swelling having increased considerably, 

 heat was applied as before; but by a larger needle, retained for 

 thirty-five minutes, this tended to diminish the pulsation, but it re- 

 turned on the third day with much pain in the tumour. On the 

 forty-fourth day after the operation, a larger heated needle than the 

 former was introduced for thirty minutes, when the pulsation sud- 

 denly stopped, and the patient felt free from pain. The tumour was 

 solid to the touch, and there was no return of pulsation in it. The 

 leg, however, soon afterwards became cedematous, mortification en- 

 sued, and the patient died on the ninetieth day after the operation, of 

 the effect of the mere pressure of the tumour. The appearance of the 

 coagulum found in the sac after death is shown in an annexed draw- 



