AND RATIO OF TnKJli ATOMIC WF.KillTS. 



25 



tions were repeated several times, the distillatiou each time being made from a clean 

 apparatus. The tube was filled by boiling under reduced pressure, and the ebulli- 

 tion after each addition of mercury was maintained for twenty oi' tliiily minutes. 

 The perfection of the vacuum was examined iu the usual way by varying the vol- 

 ume of the space left vacuous above the mercury, and measuring the correspond- 

 ing barometric height. It was proved that the residual air or va]>or in the vacuum 

 had a teusion less than the hundredth of a millimetre, which had not increased 

 measurably at the close of the experiments to be described in tliis [ia[ier. 



Since the globe a, Fig. 0, was not maintained at constant temperature, the pres- 

 sure of the gas was not constant. It was therefore impossible to make several 

 readings of pressure and temperature and take their mean. Pressure and tempera- 

 ture were therefore read simultaneously at intervals till it was thought that they 

 had attained a regular march ; then they were read finally, and the stopcock c was 

 closed. This pair of readings was adopted iu the reduction. The cover e e w^as 

 then raised till the sto})cock h of the globe could be closed. Any slight change of 

 temperature could do no harm for the stopcock c had been closed at the time of the 

 final readings of temperature and piessure. The globe was now separated from 

 the ground joint ;;., when it was ready for weighing. 



The determination of temperature depended on a thermometer numbei'ed 2053. 

 It is of Jena normal glass, and is divided into fiftieths of a degree. Its principal 

 scale is from 12° to 26°; but it has also short scales from - 0.8° to + 0.3°, from 

 49.5° to 50.5°, and from 97.5° to 100.5°. 



This thermometer I have tw'ice caliljrated. The fundamental intei'val was 

 obtained by the following observations : 

 Time, 



h. m. 

 lo 30 

 10 ii 

 10 35 

 10 37 

 10 38 

 10 40 

 10 42 

 10 43 

 At 10.44, the thermometer was nearly at the temperature of melting ice, and 



the foUowino; observations were obtained : 



Time, 

 h. m. 

 10 45 

 10 45 3° 

 10 46 

 10 46 30 

 10 47 

 10 48 

 10 49 



Thermometer 2053. 



— 0.292° 

 .300 

 .300 

 .298 

 .294 

 .292 

 .292 



