156 Trans. Acad. Sci. of St. Louis. 



The strength of the field just outside of the flame, at 

 the point occupied by the needle, was in every case in- 

 creased by the flame. The commotion of the ionized 

 molecules within the flame, decreased the permeability 

 of the space occupied by the flame. The lines of force 

 were deflected around this vertical column. The instant 

 when the combustion began is represented by the arrow 

 on the two diagrams. The effect upon the needle did not 

 continue in any case for very much more than one min- 

 ute, and it was generally somewhat less. 



The explosions of dynamite in open air produced a 

 disturbance over a very large area. In some cases as 

 many as 22 sticks of 40 per cent dynamite were laid upon 

 a long bar of wood, having a cross section of 1x1.5 inches. 

 Each stick was securely bound to the bar at each end, by 

 means of heavy binding twine. The sticks were placed 

 end on end and the explosive cap was placed in the stick 

 at the end of the column. The bar was mounted upon 

 supporting posts at a height of eight ft. above the ground. 

 No trace of the bar of wood could be found after the ex- 

 plosion, except the shattered ends projecting slightly be- 

 yond the column of dynamite. The marsh grass and iris 

 which was about 2 ft. in height was closely shaved from 

 the surface of the ground, over a distance of about 30 f% 

 on either side of the column. It was all deposited in a 

 long heap directly below the line of the column. Evi- 

 dently the rebound of the compression wave of air and 

 gas from the ground, had caused an inflow which swept 

 the grass inward and upward. No disturbance of the 

 tent, 275 ft. distant, could be detected. A screen of boards 

 was erected in front of the end of the table to protect the 

 needle, but fine fibers of silk suspended within the tent 

 showed no appreciable deflection. A window glass in 

 our cottage, having dimensions 29x30 inches, was broken 

 by an explosion of 25 sticks. The cottage was distant 225 

 ft. This does not necessarily mean that the breakage 

 was due wholly to the explosion. A glass which replaced 

 it also broke down a few weeks after being put in place, 



