PHYSICS: C. BARUS 
547 
THE DISPLACEMENT OF THE GRAVITATING NEEDLE 
IN ITS DEPENDENCE ON ATMOSPHERIC 
TEMPERATURES 
By Carl Barus 
Department of Physics, Brown University 
Communicated October 8, 1919 
1. Introductory. — In Science (50, pp. 214, 279, 1919) I communicated 
some of the early results, showing that the deflection of the needle of a 
gravitation apparatus varies in marked degree with the temperature on 
the outside of the building. I have since carried these experiments on 
for another month and the evidence has become more definitely inter- 
pretable. The work was done in a semi-subterranean room, in which 
the thermostat shows temperature variations which do not usually 
exceed a fraction of a degree. The room is large and so damp that all 
electrical excitation is excluded. Tests with radium fully confirmed 
this. Moreover the room is kept dark. The apparatus (Proceed- 
ings, 4, p. 338, 1918) placed on the north-south wall of the pier con- 
fronts an eastern 30-inch wall, at a distance of about 4 meters and the 
outside of this is illuminated by sunlight, if present, in the morning, 
only. 
2. Observations. — The observations during July and August are given 
at the bottom of the figure, the two curves being mean results of the 
a.m. and p.m. readings, respectively. The telescopic reading of the 
scale is y, so that Ay denotes the mean (static) excursion or double 
amplitude, when the attracting mass, M = 1 kgm. is passed from one 
side to the other of the attracted shot (m = 0.6 gram), at the end of a 
needle suspended by a quartz fiber. The actual excursion of the shot 
is Ax = 0.01455 Ay, so that the magnification is about 70. The figure 
shows that even these mean excursions vary enormously, from values 
much below A3; = 2 to values above 7, easily five times. If individual 
excursions were taken, ratios as high as 10 might be found, in spite of 
the practically constant room temperature. On the upper part of the 
chart I have inserted the temperature observations 6 in degrees F., 
made at Providence by the United States Weather Bureau, as well 
as the temperature variations (high minus low) of the successive 
days of the months, the same abscissas holding for all curves. 
In the earlier data there seemed to be a close association between 
the Ay and 0 curves. In the present data the regions a, b, c, d, e, belong 
