136 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1917. 



nected with the indicating needle no longer rested on the other lever 

 but had passed below. It was immediately apparent that this con- 

 dition could have been caused only by an abnormal dilation of the 

 aneroid system due to a considerable barometric depression. Under 

 these circumstances the instrument had registered a pressure much 

 below the minimum pressure inscribed on its graduated arc. 



After having put the two levers in place the instrument was placed 

 under the bell of an air pump and exposed to the vacuum. It was 

 found that the two levers changed positions when the pressure on the 

 interior had fallen to 410 millimeters of mercury. It was concluded 

 that the explosion of the shell produced in its vicinity a static de- 

 pression of 760 — 410=350 millimeters of mercury. 



From the aerodynamic formulas it appears that the immediate 

 production of this depression .will give birth to a wind having a ve- 

 locity of 276 meters per second and which will produce a dynamic 

 pressure of 10,360 kilograms per square meter on a plane surface 

 normal to the direction of its propagation. 



Such a rush of air would overturn and crush to earth persons ex- 

 posed to it. Those escaping would nevertheless suffer from the 

 brusque depression, reckoned above, which would follow. Owing to 

 this the air and carbon dioxide dissolved in the blood will be imme- 

 diately set free in small bubbles, and, if their diameters are larger 

 than those of the small arteries, they will form gaseous plugs which 

 will instantly arrest the circulation of the blood in these arteries 

 and death will occur before the re-solution in the blood on the res- 

 toration of the pressure to normal. 



The passage of the sound wave at the outset of its formation can 

 also rupture the eardrum, but its duration is extremely brief as 

 compared with that of the following depression. 



In all of the foregoing there has been only the single question of 

 the mechanical effects due to the passage of the explosive from the 

 solid to the gaseous state. The occurrences of the war have thrown 

 light on the pathological role which the gases produced or liberated 

 in detonation have come to play. Without wishing to enter on the 

 study of projectiles designed for asphyxiation of the enemy we may 

 remark that most of the nitro explosives employed in charging shell 

 disengage notable proportions of carbon monoxid. Although the 

 toxic power of this gas is relatively great, it may be observed here 

 that it is not freed except when the explosion occurs out of contact 

 with the air. This will, for example, be the case where a projectile 

 is buried and exploded in the earth or a shell is exploded in a habi- 

 tation of small size. In all other cases the carbon monoxid is imme- 

 diately burned by the oxygen of the air in such manner that in 

 reality only carbon dioxid is observed. It is known that man can 



