244 PHYSICS. 



and 2 or 3™™ in diameter, closed at top and carefully calibrated. Below, 

 tlie bulb connects with a straight tube SO*^™ long, a lateral tube opening 

 into it just below the bulb and leading upward to the pump. The ca- 

 pacity of the bulb above the lateral opening is ascertained by weighing 

 the mercury which tills it. Thus the ratio of the volumes of the bulb 

 and of the small tube above it is known. The long tube is connected 

 at its lower end with a reservoir of mercury by means of a rubber tube, 

 so that when this is raised the gauge may be filled with mercury. After 

 the vacuum has been made in the i^ump, of which the gauge forms a 

 part, the reservoir is lifted and the mercury rises in the long tube until 

 it passes the mouth of the lateral tube and seals off the air in the bulb. 

 As the mercury fills the bulb, the air collects in the small tube, and the 

 pressure under which it exists is the difference of level of the mercury 

 in this tube and the side tube. Knowing the volumes and the final press- 

 ure the initial ])ressure is given by Marriotte's law. Mr. Crookes regards 

 it reliable to the millionth of an atmosphere, 0.0007CO™™. Warren de la 

 'Rue limits its indications at 0.00005"^™.— (Aww. Chim. PJiys., Y, xix, 231, 

 February, 1880.) 



Amagat has studied elaborately the variation of gaseous bodies from 

 the law of INIarriotte at high pressures, exact measurements being made 

 of the changes in volume when the gas sustained a mercury column 

 over one-fifth of a mile high. The shaft of the Verpilleux coal mine, 

 near St. Etienne, 327™ in depth, was chosen, the experiments here being 

 confined to nitrogen gas. A jiowerful and specially constructed pump 

 forced mercury at the same time up the manometer tube and into the 

 tube containing the gas. Since both were carefully calibrated, the meas- 

 urement in the former gave the i^ressure and in the latter the volume. 

 In nitrogen the compressibility increases slowly and reaches a maximum 

 at about 65 atmospheres. Then it decreases equally slowly, reaching a 

 normal figure at about 91 atmospheres. Finally it decreases rapidly, 

 till at 430 atmospheres the volume is five-fourths of that required by 

 Marriotte's law. This law of nitrogen being ascertained, the manometer 

 tube was replaced by a nitrogen tube and the other gases compared 

 with that. Air, oxygen, hydrogen, carbonous oxide, ethylene, and marsh 

 gas were examined up to 400 atmospheres. The results are given graphi- 

 cally, the abscissas representing pressures and the ordinates the difl"er- 

 ences between the product of the volumes by the pressures and unity, 

 i. e., to the deviations from Marriotte's law. Hydrogen only does not 

 exhibit a minimum of volume and pressure product. — {Ann. Chim. PJiys., 

 Y, xix, 345, March, 1880.) Cailletet has also studied the law of the com- 

 l)ression of nitrogen. He used a steel laboratory tube, within which 

 \vas a piezometer tube containing the gas. To the laboratory tube was 

 attached a tube of soft steel 250°^ long, rolled upon a wooden cylinder 

 2™ in diameter. The laboratory tube was supported by a steel wire 4™"^ 

 diameter, carefully graduated. The gas tube being put in place, the 

 apparatus was filled with mercury and lowered by a windlass into an arte- 



