184 hertz's eesearches on electrical waves. 



preciable disturbing eifect. The end wall, from which the waves were 

 to be reflected, was of solid sandstone, with two doors in it, and the 

 numerous gas pipes attached to it gave it, to a certain extent, the 

 character of a conducting surface, and this was increased by fastening 

 to it a sheet of zinc 4 meters high and 2 meters broad, connected by 

 wires to the gas-pipes and a neighboring water-pipe. Special care was 

 taken to provide an escape for the electricity at the upper and lower 

 extremities of the zinc plate, where a certain accumulation of electricity 

 was to be expected. 



The primary conductor was the same that was employed in the ex- 

 periments last described, and was placed at a distance of 13 meters from 

 the zinc plate, and therefore two meters from the wall at the other end 

 of the room. The conducting wire was placed vertically, so that the e. 

 M. F.'s to be considered increased and diminished in a vertical direction. 

 The center of the primary conductor was 2.5 meters above the floor of 

 the room, which left a clear space for the observations above the tables 

 and benches. The point of intersection of the reflecting surface with 

 the perpendicular from the center of the primary conductor will be called 

 the point of incidence, and the experiments were limited to the neigh- 

 borhood of this point, as the investigation of waves striking the wall 

 at a considerable angle would be complicated by the differences in their 

 polarization. The plane of vibration was therefore parallel to the reflect- 

 ing surface, and the plane of the waves was perpendicular to it, and 

 passed through the point of incidence. 



The secondary conductor consisted of the circle of 35 centimeters 

 radius, which has been already described. It was movable about an axis 

 through its center perpendicular to its plane, and the axis itself was 

 movable in a horizontal plane about a vertical axis. In most of the 

 experiments the secondary conductor was held in the hand by its 

 insulating wooden support, as this was the most convenient way of 

 bringing it into the various positions required. The results of these 

 experiments however had to be checked by observations made with 

 the observer at a greater distance from the secondary, as the ueighbor- 

 liood of his body exerted a slight influence upon the phenomena. The 

 sparks were distinct enough to be observed at a distance of several 

 meters when the room was darkened, but when the room remained light 

 tliey were practically invisible even when the observer was (piite close 

 to the secondary. 



When the center of the secondary was placed in the line of incidence 

 and with its plane in the plane of vibration, and the air space was 

 turned first towards the reflecting wall and then away from it, a con- 

 siderable diflierence was generally observed in the strength of the sparks 

 in the two positions. At a distance of about 0.8 meter from the wall 

 the sparks were much stronger when the air space was directed towards 

 the wall, and its length could be adjusted so that while there was a 

 steady stream of sparks when in this position, they disappeared entirely 



