120 Mr. D. Gilbert on Ventilation. 



like extraneous air ascending, would equally retard the draft; 

 and the effects of irregular, temporary movements of the 

 atmosphere will be rendered insensible. These appear to be 

 the chief advantages derived from earthen tubes, very fre- 

 quently seen on the tops of chimneys, which in most cases 

 make but a very insignificant addition to the length of the 

 flue. 



Those stoves or fire-places are constructed on the best prin- 

 ciples which throw the greatest quantity of radiant heat into 

 the rooms they are intended to warm, and at the same time take 

 away the least quantity of heated air. 



In concluding this paper it must be remarked, that although 

 the formulae deduced from the height of an uniform atmo- 

 sphere, and from the velocity of air rushing into a vacuum, 

 are not perfectly correct, under the actual circumstances ; yet 

 they have been ascertained to approach sufficiently near to 

 the truth by experiments on the supply of air afforded to blast 

 furnaces. Differences, much greater than any to be appre- 

 hended in these expressions, will arise from the state of the 

 weather. Thus, in a calm it is probable that the rarefied 

 column of air, ascending from a stack, must add somewhat to 

 its virtual height ; while, on the contrary, a rapid horizontal 

 motion of the atmosphere will each instant present fresh ob- 

 stacles against the ascent of the heated vapour, and render 

 the draft less powerful. 



Art. XI. On the Effects produced on the Human Coun- 

 tenance, by Paralysis of the different systems of Facial 

 Nerves. By John Shaw, Esq. 



In the last Number of this Journal, an account of the anatomy 

 of the nerves of the face, in several animals, was given, and 

 some experiments were (detailed, to shew that very different 

 results ensued when the nerve, called respiratory of the face 

 was cut, from those which followed the division of the 5th pair. 



A few cases will now be related, to prove that the changes 



