VOL. LIT.] VHILOSOPHICAL TRANSACTIONS. 147 



tained there, and the space it occupies prevents as much of the external air being 

 received into the lungs as its own quantity. As, from their incessant motion, 

 injuries to the lungs are not easily removed, when once a rupture is made, every 

 fit of coughing or other violent exertion extravasates more air. Hence the rup- 

 ture still continuing, and probably increasing, more and more air becomes extra- 

 vasated, till, as in the present case, the quantity becomes so great, as not only 

 to impede the course of the blood through the lungs, but the internal pressure 

 of the extravasated air prevents the ingress of a quantity of fresh air, sufficient 

 to cool and attenuate the blood. In fact, a small part only of the lungs is em- 

 ployed; as the extravasated air, though sti'Un an elastic state, by no means an- 

 swers the purposes of fresh air in respiration ; as the former, by its confinement 

 in the lungs, is very soon divested of its vivifying spirit, that principle which is 

 soon destroyed in animal bodies, and which some chemical physiologists have 

 supposed to be an acid nitrous gas, and is most essential to human life. Hence, 

 in a very short time, the effects are too obvious to be mentioned; and death must 

 soon follow, as in this instance. 



XLIV. Considerations to prevent Lightning /rom doing Mischief to great fVorks, 

 High Buildings, and Large Magazines. By Mr. Wilson, F.R.S. p, 247. 



Long experience since the discovery by Dr. Franklin, has now established a 

 truth among philosophers, that lightning, like the electric fluid, passes more 

 fi-eely through iron, copper, and other metals, than through dry wood, stone, 

 or marble. Instances of this truth are innumerable: and to be convinced of it, 

 we need only trace the late violent effects of lightning on St. Bride's church, and 

 the houses in Essex-street, &c. For, on examining these buildings, it appears 

 that there are certain thick bars of iron, through which the lightning has passed, 

 without producing any visible effects; and, on the contrary, in certain parts 

 where the junctions of those bars with the stone, or wood, are made, there the 

 lightning, rushing from the iron, has broke the stone to pieces, and shivered the 

 wood. From the like experience we also learn, that if the iron is too slender for 

 conducting tiie lightning, it is either dashed into pieces, or exploded like gun- 

 powder; just in the same manner as we are able, by the electric power, to break 

 and dissipate in vapour a very slender wire. Bars of metal, of a proper thick- 

 ness, and conveniently disposed, seem therefore necessary for the security of such 

 buildings. 



It is to be noted, that the mischiefs caused by lightning are not always owing 

 to its direction from the clouds to the buildings or other eminences, and thence 

 to the earth; but sometimes, on the contrary, from the earth, buildings, and 

 other eminences, to the clouds. For the principle on which its direction depends, 

 appears to arise from the restoration of a certain equilibrium, in a subtile and 



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