548 
PHYSICS: C. BARUS 
together, though the A^; curve follows the 6 curve with a lag of one or 
more days. A far better agreement in sense, not quantitatively always, 
now appears between the Ay and M curves, and here in the given time 
scale, practically without a lag. To bring this to the eye more clearly, 
I have indicated the corresponding successive cusps in both curves with 
the same numbers 1 to 23. The agreement is in fact as close as it can 
possibly be, remembering that M holds for twenty-four hours of the day 
and Ay only for the daylight interval of observation. In the same 
way the a.m. and p.m. curves differ enormously when there is sunlight, 
and very little in damp cloudy rainy weather {R in curve). In general 
and apart from details, the a.m. excursions reappeared in a subdued 
form in the p.m. results. |#ftS?LS 
3. The needle in vacuum. — In Science I also communicated a series 
of results since much amplified, showing that for a case of two glass 
plates spaced by an impregnated wood frame, the initial attractions 
could be diminished to about one-third of their value by exhausting the 
case. The excursions diminished with the pressure, at a mean rate of 
1%, per mercury centimeter of pressure. The glass plates in this case 
were about 1.8 cm. apart, inside. In case of the plenum the general 
character of the a.m. and p.m. excursion did not essentially differ from 
the graphs for apparatus I. 
