Translation o/" Key's Essat/s. 63 



if it be pushed some distance into the mouth, it will suddenly 

 rise up again, which would assuredly not happen if the air 

 were not thicker than on (d Vescart) one side of the cannon 

 where the flock of wool descends readily. These reasons 

 though not gross, are nevertheless so palpable that they must 

 convince every one that heat has thickened the air just above 

 the muzzle of the gun. But if it has thickened it before the 

 mouth, what, I pray you, must it have done at the bottom of the 

 bore next the ball ? Unquestionably when that comes out 

 after it is cold, you will see it more inclining to a whitish hue 

 than before it was heated red, as if the thickened and adhe- 

 sive air gave it that colour, which in time tarnishes and wears 

 off", especially in a damp place, since the surrounding air, 

 moistening that which adheres to the ball, reduces it to its ori- 

 ginal state. By way of dessert I will serve up one remark to 

 the reader, which perhaps will be to his taste. They who 

 worthily practise medicine are sometimes called in to visit an 

 asthmatic patient, who panting in bed in a hot chamber, fetches 

 his breath with great difficulty, which the physicians observing, 

 they have the window thrown open, conduct the patient to it, 

 and make him inhale the outer air, to his great relief. If yoa 

 ask these gentlemen whence the sick man receives so imme- 

 diate comfort, they will tell you, it is because the air of the 

 chamber being too hot cannot furnish that necessary refresh- 

 ment to the heart, which the external air by its coolness af- 

 fords. But gentlemen, my honoured colleagues, having unde- 

 ceived myself on this point by the preceding meditations, suffer 

 me, I pray you, to undeceive you also. It is not the heat of 

 the air of the chamber that occasions the panting, as not being 

 capable of sufficiently refreshing the heart, but rather it is its 

 thickness, which retards its course across the obstruction {lite- 

 ral) of the lungs, so that it cannot furnish the heart regularly 

 (rt temps) with sufficient matter for the generation of the vital 

 spirits, which fresh air being more subtle, can better effect. 

 Now, that you may not fancy I advance this without reason, 

 observe the feverish patient who lies in the same chamber, 

 wliom the confined air sufficiently rf;freshes, although he has 



