Vol. 8, 1922 
Physics: C. Barus 
13 
islands need not have been stable. This aspect of the coral-reef problem 
is examined in an essay submitted to the Geological Society of America 
for publication in its Bulletin. 
The foregoing discussion will be presented in greater detail in the Annals 
of the Association of American Geographers. 
1 J, Macgillivray, Narrative of the Voyage of H. M. S. Rattlesnake, London, 1852. 
2 vols. See i, 182; ii, 72. 
2 B. H. Thomson, "New Guinea: Narrative of an Exploring Expedition to the Louis- 
iade and D'Entrecasteaux Islands, "Proc. Roy. Geogr. Soc, 11, 1889 (.525-542). 
3 A. G. Maitland, "Geological Observations in British New Guinea," Queensland 
Geol. Surv. Pub., 85, 1892. "Salient Geological Features of New Guinea," Journ. W. 
Austral. N. H. Soc, 2, 1905 (32-56). 
4 "Problems Associated with the Study of Coral Reef," Set. Monthly, 2, 1916 (565). 
EXPERIMENTS WITH THE VACUUM GRAVITATION NEEDLE^ 
By Carl Barus 
Department of Physics, Brown University 
Communicated November 11, 1921 
1. Apparatus. — At the end of the previous summer's experiments, a 
form of apparatus was installed capable of exhaustion and containing a 
gravitation needle made of wires as thin as possible (bronze, .24 mm. in 
diameter) compatibly with the lead weights, m, at the ends. The object 
of this was to diminish the radiation effect to an inferior limit, always re- 
membering that the lateral area of the shots m is necessarily in presence. 
The narrow case was a rectangle of brass with reentrant sides, into 
which plates of thick glass could be sealed with cement free from air leakage. 
Each attracting weight M had a mounting quite independent of the case 
and could easily be moved between stops from one side to the other of it 
by a crank -like arrangement. 
The half silver method of reading the deflections of the needle and other 
details were retained, with the scale distance, L = 447.5 cm. 
The masses of the attracted lead balls at the end of the filamentary 
needle were m = .6295 grams each, though the quartz fibre would have been 
strong enough to hold a larger mass to advantage. The distances R of the 
