PHYSIC8. 570 



ance. Oil parsing into the bell jar a current of dry air, aiid adjusting 

 to zero by a suitable tare, the apparatus is ready for experiment. On 

 introducing a current of dry hydrogen the balloon rises and the weights 

 are adjusted nearly to equilibrium. The current of gas is then arrested 

 and the exact balance obtained. The hydrogen is then replaced by 

 illuminating gas and the experiment repeated. A third experiment is 

 made with dry carbon dioxide. From the data thus obtained the den- 

 sity of the coal gas is calculated. (Jour. Phys., January, 1883, II, II, 29.) 



Cooke has proposed a simple method of calculating the correction 

 required for the buoyancy of the atmosphere when the volume of the 

 body weighed is unknown. If 30 inches be assumed as the barometric 

 standard, a variation of 0.1 inch will affect the buoyancy by one three- 

 hundredth. Again, assuming 27° C. as the temperature standard, 

 which is 300° on the absolute scale, a variation of one degree will also 

 affect the buoyancy by one three-hundredth ; i. e., one degree variation 

 in temperature produces the same effect on the buoyancy as a change 

 of 0.1 inch in the pressure. The correction for temperature, which is 

 the more important of the two, is effected by simply adding to the 

 observed height of the barometer, u'iven in tenths of an inch, the differ- 

 ence between 27° C. and the observed temperature. By means of a few 

 weighings, taken under as great a variation of temperature and press 

 ore as possible, the quotient of the difference in weight by the cor- 

 rected barometer difference gives the difference in weight corresponding 

 to one tenth of an inch difference in pressure. By multiplying now the 

 difference between 3U0 and the corrected barometric heights by the con- 

 stant thus obtained, and adding or subtracting this product, as the case 

 may be, to or from the observed weights, the weighings are all reduced 

 to the standard of 30 inches. (Am. J. Sei. } July, 1883, III, xxvi, 38.) 



Edelmann proposes to determine the relative density of two gases by 

 causing two columns of these gases of the same height to act on an 

 elastic membrane, the displacement of which is very accurately meas- 

 ured. The membrane employed is like that used in an aneroid barom- 

 eter, mounted on a metallic box 30 centimeters in diameter, the two 

 sides of the box communicating with vertical tubes about 2 meters long, 

 containing the gases. The movement of the membrane operates a lever 

 carrying a mirror, by the aid of which, with a telescope and scale, very 

 slight displacements may be read. In the author's apparatus one-tenth 

 of a millimeter on the scale corresponds to less than one millionth of an 

 atmosphere in the box. (Carl. Rep., xvn; J. Phys., June, 1883, II, ii, 

 285.) 



Amagat has published four memoirs upon the compressibility of gases. 

 In the first he considers certain objections raised against his apparatus 

 or method ; in the second he treats of the compressibility of air and 

 of carbon dioxide from one to eight atmospheres pressure and from 20° 

 to 300° 0.; in the third the compressibility of rarefied air, hydrogen, 

 and carbon dioxide is considered; and the fourth is on a new form of 



