AND RATIO ()!•' TllKlli ATOMIC WKICIITS. 15 



The cover was then soldered in place, the cylinder was (|iiite tilled with water, and 

 tiie iiil)i>er sto{)per // was iiiserte(l. 'I'o /' were connected the tnhes (j and //. On 

 the tube // was a mark: g was graduated in tenths of cubic centimetres. To the 

 ui)i)er end of / was attached some simple device for varyi'iii; the pressui-e of the air 

 in it. These tubes were filled with water to the level of the mark //. The tube // 

 is intended to act as a manometer sliowing' the pressure on tiie water in tiie 

 cylinder. 



Let us suppose, for a moment, the temperatni'e of the watei' in the cylinder 

 to be constant ; if we alter the volume of the globe, but keep the pressure on 

 the water constant by watching the manometer, and introducing or removing water, 

 we shall have a measure of the change of volume of the globe. 



The manipulation is accordingly as follows: We bring the level of the water 

 iu the manometer tube // exactly to the mark, and note the reading on the graduated 

 tube g. Then we exhaust the globe, and keep the pressure constant in the cylinder 

 by introducing water into it from the graduated tube, which we read again. The 

 difference of the two readings is the change of volinne of the globe, provided the 

 temperature of the water is constant. If now air is admitted, and the alternate 

 readings are repeated at nearly e.pial intervals, we can eliminate the effect of slow 

 changes of temperature and determine the change of volume of the globe with 

 accuracy. 



As to the convenience of the method it may l)e said that, when the globe was 

 not filled with water, the whole operation of putting the globe in place, soldering 

 the cover, making a sufficient numVier of determinations, and taking out the globe, 

 could be finished in two hours. When the globe was filled with watei", the intervals 

 between readings were shortei-, but the time required to fill the globe and to emi.ty 

 it again was considerable. Most of the detei-rainations wei-e made in this latter way ; 

 three determinations wei-e the work of nearly a whole day. The method, as wdl 

 be seen from the following example, gave concordant results ; it also gave concor- 

 dant results when applied to the same globe on different days. 



UETERMINATION OF THK COMPRESSION OF OI.OBE NO. I. 

 Time. PresMiie. Burette. Differences. 



3 h. 48 m. 743 mm- 4-02 cc. 



3 " 53 " 30 " 2.77 " 7'3 mm. 1.22 cc. 



3 " 58 " 743 ': 3.96 ;; 7 IS ;; ; 23 ^^ 



4 " 04 " 26 " 2.70 717 1-22 ^^ 



4 " 10 " 743 " 3.88 '; 7-6 ;; 1.21 ^, 



4 " ,6 " 28 " 2.63 715 '-22 



4 " 21 " 743 " 3-82 " 



The compression of each globe due to a difference of internal pressures meas- 

 ured by seventy-six centimetres of mercury is given in the following table : 



