994 



SCIENCE. 



[N. S. Vol. XV. No. 390. 



to this subject, as I think that some reform 

 is greatly needed. I agree with him in all 

 that he says except that I do not think the 

 term 'measurement' is the proper one to take 

 the place of the common title 'weights and 

 measures.' Under the latter title is always 

 understood a list of the units and their equiva- 

 lents, and therefore the term 'measurement' 

 does not apply. In view of the fact that the 

 units of weight are measures quite as well as 

 the units of length are, it seems to me a 

 much better title would be simply 'measures,' 

 and I would urge the adoption of that title 

 in place of the word 'measurement,' suggested 

 by Dr. Goodspeed. 



Carl Heeing. 

 Philadelphia. 



SHORTER ARTICLES. 



DIVERGENCE OF LONG PLUMB-LINES AT THE 

 TAMARACK MINE. 



In September last two very long plumb-lines 

 were hung in No. 5 shaft of the Tamarack 

 Mine at Calumet, Michigan. They were 4,250 

 ft. in length, being longer than in any pre- 

 viously recorded instance. They were of No. 

 24 piano wire and the bobs were of cast iron, 

 weighing fifty pounds each. Great care was 

 taken that there should be no interference 

 from projecting objects nor from dropping 

 water, of which indeed there is not a great deal 

 in the shaft. Measurements between the lines 

 taken at surface and at their lower extremities 

 showed a divergence to the amount of 0.11 

 ft. A divergence of 0.07 ft. remained after 

 the western wire had been moved about 1.25 

 ft. further west to ensure its freedom from 

 obstacles. Thinking that the air pipes which 

 run down the western end of the shaft might, 

 through magnetic action on the bob nearest 

 them, be causing this divergence, I advised 

 the use of lead bobs in a plumbing of No. 2 

 shaft, which took place a little later. Al- 

 though the length of the .lines in No. 2 was 

 about 120 ft. less than when they hung in 

 No. 5, and although the lead bobs were used, 

 there was yet a divergence of 0.10 ft. 



The publication about this time in the 

 Houghton Daily Mining Gazette of the fact 

 that a divergence had been observed at- 



tracted wide attention, and brought forth 

 many attempts to explain its existence. 

 Those immediately cognizant of the condi- 

 tions had no satisfactory theory to offer. One 

 of the explanations was that the divergence 

 was due to the greater attraction of the ma- 

 terial at the end of the shaft for the bob hang- 

 ing nearest it. It is remarkable how many 

 engineers and other trained persons held to 

 this theory. There seems to exist a general 

 lack of appreciation of the forces of gravita- 

 tion, except in the single instance of the force 

 between the earth and objects upon it. It 

 is of course true that the attractions on either 

 bob toward the ends of the shaft are different, 

 the stronger being toward the end nearest 

 to which it hangs. Furthermore, these dif- 

 ferences of attraction tend to diverge the 

 lines. Their amounts, however, are in this 

 case so insignificant as to put them quite out 

 of consideration in attempting to explain the 

 divergence. Their sum is only a few hun- 

 dredths of a grain, and the consequent diver- 

 gence only about 0.001 ft. 



Professor Hallock, of Columbia University, 

 suggested the theory of repulsion between like 

 poles at the lower extremities of the wire, but 

 afterwards modified this to include repulsion 

 between like consequent poles distributed 

 along the wires. 



Permission having been granted nie to carry 

 on further experiments in No. 4 shaft of the 

 Tamarack Mine, there were hung in this shaft 

 bronze wires No. 20 B. & S. gauge, carrying 

 CO-pound lead bobs. These lines were ap- 

 proximately 15 ft. apart and 4,440 ft. in 

 length. By a simple system of triangulation 

 the distance between the mean positions of 

 their lower extremities was determined, while 

 the distance between them at surface was 

 directly measured. It is thought that these 

 distances were compared with an error not 

 greater than 0.003 ft. A small convergence 

 of 0.028 ft. was observed. The steel wires 

 were then hung in the same position at the 

 top, and the positions at the bottom observed, 

 both with lead and with iron bobs. The brortze 

 wires were hung a second time, but somewhat 

 nearer together, and were found practically 

 parallel. The steel lines showed a slight con- 



