416 



SCIENCE. 



[N. S. Vol. XXIII. No. 585. 



During the investigation of the cause of 

 divergence of long plumb lines hung in 

 the No. 5 shaft of the Tamarack Mine^ 

 attention was drawn to the old Cornish 

 method of plumbing a shait by dropping 

 a spherical shot, the vertical being assumed 

 as the line joining the point of suspension 

 with the point of striking at the bottom. 

 A rough calculation of the pi'obable easterly 

 deviation which might be expected of a 

 body dropping from surface to the foot of 

 the lines, forty-two hundred feet, led to the 

 announcement that it was in the neighbor- 

 hood of four feet. This is obtained by 

 taking the difference in velocity between 

 points on the two cylinders about the 

 earth's axis, one including the small circle 

 of latitude and the other that through the 

 foot of the plumb lines, and multiplying by 

 the seconds allowed for the fall. 



A deviation admitting of consistent meas- 

 urement in feet was impressive enough to 

 create a demand for an opportunity of wit- 

 nessing it, and an experiment was devised 

 to gratify this desire. It was performed 

 at the close of a certain day's 'plumbing' 

 in No. 5 shaft and consisted in suspending 

 a steel sphere by a thread at the collar, get- 

 ting it as quiet as possible, then burning 

 the thread while observers below watched 

 for its striking a prepared clay bed. 



It was a little over five feet from point 

 suspension of sphere east to shaft timbers. 

 In a vacuum between sixteen and seventeen 

 seconds would be occupied in the fall. The 

 ball failed to appear at all. 



Another sphere hung in the center of the 

 shaft compartment about three feet from 

 the eastern timbers, when dropped, also 

 failed to appear below. Afterward a 

 sphere, presumably this one, was found 

 lodged about eight hiindred feet from sur- 



' See Science, Vol. XV., page 994. Also Engi- 

 neering and Mining Journal, April 26, 1902. 



face. Further experiments were not then 

 feasible. 



Crude as was the whole proceeding and 

 devoid of serious purpose, it yet drew the 

 attention of those concerned to the possi- 

 bilities offered by the deep vertical shafts 

 of the copper district of Michigan for the 

 investigation of easterly deviation. 



The author suggests that an accurate 

 mapping of the path of a falling body be- 

 neath the surface might possibly afford in- 

 teresting data bearing on the distribution 

 of the earth's matter. He hopes at a sub- 

 sequent time to present a properly elabo- 

 rated plan of investigation of this path. 



A Device for producing an Instantaneous 

 Arc at any Phase of an Alternating Cur- 

 rent: Henry Crew, Northwestern Uni- 

 versity. 



The essential features of this instrument 

 are as follows: (1) A pair of electrodes, 

 one of which has a motion of pure trans- 

 lation; the other, a motion of pure rota- 

 tion. (2) The rotating electrode is driven 

 on the shaft of a synchronous motor. (3) 

 The arc is fed by the same transformer 

 which drives the motor. (4) The phase of 

 contact between the movirig electrode and 

 the fixed one is read off on a divided circle. 

 The object of this device is to obtain a 

 comparatively cold ( ? ) carbon arc in the 

 neighborhood of zero-phase. The region 

 between the poles of a continuously oper- 

 ated carbon arc shows no carbon bands, in 

 its spectrum, at zero phase. But a carbon 

 are of the type indicated above shews the 

 carbon bands at the lowest phases that can 

 be examined, say, from 0° to 2°. The ex- 

 planation of this difference lies probably 

 in the fact that, owing to the greater heat, 

 the current of the continuous arc at small 

 phases is carried by the ions of the metallic 

 im.p\mties ; while in the discontinuous (or 

 instantaneous) arc the conduction is made 



