Chemistry and Physics. 227 
protected with great care from air currents, or changes of tempera- 
ture. The instrument was so susceptible to disturbing influences, 
that it was set in motion by a railway train passing at a distance 
2. 
. 
of about a mi 
case a change o 1 of a second of are would be perceptible, or 
would alter the scale-reading ‘1 of a millimeter. New the calcula- 
tions of Dr. C, eters show that the effect o on 
oa h ff f the mo 
when at its maximum produces a deviation of -0174", or doubling 
this amount for the difference on the two sides of the meridian 
045", or thirty-five times the amount perceptible with this instru- 
ment. The sun in like manner would produce a variation of -016". 
Hence it seems possible by this means to weigh directly the masses 
of the sun and moon in terms of the earth, and hence determine 
their distances. The deviation would change its sign whenever 
these bodies crossed the meridian, and hence if it could be accu- 
rately determined, would afford a means of measuring the time re- 
quired by gravity to pass from the sun to the earth. Jf course, 
such observations would be greatly disturbed by variations of 
temperature, shaking of the ground, and many other causes; an 
hence should be conducted in caves at a considerable distance from 
human habitation.— Pogg. Annal., cl, 134. E. 0. P. 
6. Specific heat of Gases under constant volume and under con- 
stant pressure—M. AmaGat has measured that most important 
mes, were it not for the oscillation of the gaseous mass at the ori- 
fice, discovered and studied by M. Cazin. This complication is 
phere, and determining its pressure immediately after its reduction 
in volume, The initial and final volume being determined with- 
~ difficulty, it only remains to apply the formula of Poisson, 
Cc 
ae ’ in which the exponent £ is the unknown quantity. 
* 
