Junk 20, 1902.] 



SCIENCE. 



995 



vergence. Subsequently the bronze wires with, 

 lead bobs were hung in No. 5 shaft in the 

 same position, as nearly as might be, as was 

 occupied by the steel wires in September. 

 The divergence was greater, amounting this 

 time to 0.141 ft. The results are exhibited 

 in the following table: 



The data shown in the table seemed to af- 

 ford ample experimental proof that neither 

 gravitation nor magnetism could account for 

 the divergence originally observed. Further, 

 it seemed that the results pointed clearly to 

 the currents of air in the shafts as the dis- 

 turbing cause. 



Until No. 5 shaft is connected with other 

 portions of the mine its ventilation is ac- 

 complished by dividing it into two parts by 

 means of a tight casing which sets off one 

 compartment and the ladder-way, at the west- 

 ern end of the shaft, to serve as an air chim- 

 ney for the up-cast draft. At the time of the 

 September and January plumbings there ex- 

 isted at different levels a number of open- 

 ings in this casing. The west wire hung in 

 the air chimney, and these openings permitted 

 a rush of air from the down-cast side into 

 the up-cast portion, the effect of which would 

 be to move the west wire toward the west and 

 thus produce a divergence. To make the 

 proof as complete as possible it was decided 

 to hang the bronze wires once more in this 

 shaft, but to hang the west one in the com- 

 partment next the air chimney, rather than 

 in it. It seemed that if both wires were hung 

 in the down-cast portion the divergence ought 

 to disappear. Moreover, communication be- 

 tween the air chimney and the down-cast 

 portion was carefully stopped off as far down 

 as the extent of the wires, and, to further pre- 



vent circulation, the shaft was covered at the 

 top as soon as the wires were in position. 

 Since a considerable difference in temperature 

 exists between the bottom of the shaft and 

 the surface, it was not possible to stop all cir- 

 culation. There remained a considerable 

 convection circulation whose down-cast por- 

 tion was concentrated along the casing above 

 referred to. The measurements between the 

 wires were, at surface 11.944 ft., at bottom 

 11.962 ft., showing a divergence of 0.018 ft. 

 This divergence was easily accounted for by 

 the convection current just described. 



The difference between the divergence of the 

 steel wires hung in this shaft in September, 

 and of the bronze ones in January is explained 

 by the fact that the circulation in the warmer 

 weather of September was much less vigorous 

 than in January and, further, that the steel 

 wires afforded the smaller surface to be acted 

 upon. 



The question of air currents had been con- 

 sidered early in the experiments. That they 

 could account for the divergence was very 

 slowly admitted by the observers, inasmuch 

 as it was difficult to believe that currents of 

 air coidd be of the steadiness, in both volume 

 and direction, which would be necessary to 

 permit the constancy which was observed in 

 the mean positions of the lines. The mean 

 positions were observed on scales, placed close 

 to the wire. Most of the time scales divided 

 into sixteenth inches were used. For hours 

 at a time the variations of the mean posi- 

 tion of a wire would not exceed three or four 

 tenths of a scale division. The mean posi- 

 tion was determined by drawing the wire 

 aside and allowing it to vibrate, as in deter- 

 mining the resting point of a balance by the 

 method of vibrations. 



The responsibility of the air currents once 

 admitted, it was found by studying the con- 

 ditions in No. 2 shaft that the divergence 

 there observed could be satisfactorily ex- 

 plained. The shaft is down-cast and the air 

 leaves it at the west end to reach the mine. 

 The small convergence observed in No. 4 

 shaft can likewise be accounted for by the 

 swirl of the currents as they enter this shaft, 

 which is up-cast. The contour of the walls 



