Deivar's Method of producing High Vacua. 



503 



The readings in the first row (t) give the time in minutes 

 from the first application of the liquid air, those in the second 

 row (h) the height in millimetres of the mercury in the 

 gauge. The values in the third row (p) are obtained by 

 subtracting the figures in the second row from 773, the 

 atmospheric pressure in millimetres o£ mercury. In the last 

 row are the values of p — p , the excess of the pressure at any 

 instant over the final pressure. 



These last figures were plotted as ordinates on semi- 

 log;! rithmic paper, with the corresponding values of the time 

 as abscissre (fig. 2, p. 504). It was then found that the points 

 lay on a straight line, showing that the pressure was connected 

 with the time by the relation 



log(>-p )=A-Ai, 



(iii.) 



where X is a constant whose value in this experiment is 0*128. 

 Similar results were obtained in the experiments numbered 

 2, 3, & 4. It is not necessary to give in full the readings in 

 these cases, as they are represented in the diagrams (fig. 2), 

 and the results in all four cases are summarized in Table III. 

 The values of X were found from the inclination to the axes 

 of the straight lines in the diagrams. It will be noticed that 

 the value of X is approximately the same in each experiment, 

 the mean value beino- 0*406. 



Table III. 







Reading 



Heading 



Final 









Initial 

 Yoliuue. 



after 1 min. 



after 4 min. 



Reading. 



A. 



\. 



















h. 



P~Po- 



h. 



P -Po- 



h. 



Po- 







I.... 



33-5 c.c. ] 



at I 



773 mm. J 



400 



193 



583 



10 



593 



180 



2-714 



•423 



II.... 



70-8 c.c. ] 



at I 



772 mm. J 



250 



13G 



377 



9 



386 



386 



2 - 555 



•421 



III. ... 



93-4 c.c. | 



at I 



772 mm. J 



218 



126 



330 



14 



344 



428 



2-480 



•380 





















IV.... 



125 c.c. | 

 at !■ 



165 



112 



265 



12 



277 



495 



2-443 



•394 





772 mm. J 



















A = height of mercury column iu mm. 

 p=pre3sure in apparatus in mm. 



