.•u 



DEN.SITIKS (iK oXYCKNiAMt llYimocKN 



>N Q, 



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VS 



I''j<;. 12. — Mouiilinj; 

 fcrcnlial manomeler to 

 lain its piisition utxiislu 



to !v pressure <»f a few millioiiths of an atmosphere, hy- 

 (Irogen was admitted to alxiut the atmosplieric pressure, 

 and this ct>iinectiiii; tube was fused off, so that the hydro- 

 s;eii was now of unalterable mass. Tiie cylinder con- 

 taining the globe was then deeply ct)vered Avitli melting ice, 

 IVoiii w liich the tube carrying the manonieterwas protected, so 

 that it slioiild not be disturbeil. The manometer w;is also 

 coyered with powdered ice, and examined througii an opening. 

 The open bi-anch of the manometer was connected to the 

 syphon barometer and also to a contriyance for micrometri- 

 cally regulating the pressure of the air in this connecting tube, 

 seen at e. Fig. 1 1 . The two leyels of the mercury in the sy]>hon 

 baionieter were in the same yertical, and \yere suri'ounded with 

 water kept well stirred by a current of air ; tempei-atui-e was 

 determined with the thermometer numbered 2053. 



While the differential manometer was covered with ice, 

 it was not easy to adjust the volume of mercuiy in it so that 

 tlie two surfaces shoidd be tangent to the two platinum points 

 at once. Accordingly, two pressures were alternately meas- 

 ured which should biing the surface h to the I'ight-liand point, 

 and then the surface c to the corresponding point. Tlie mean 

 would be the pressure which would make both surfaces tan- 

 gent to the two points at the same time, provided the volume 

 t>f mercury wei'e properly adjusted. 



The following determinations of the jircssine retpiireil to 



produce equilibrium of the gauge were made ; all the readings 



are corrected for expansion of the mercury ;iiid of the 



uf J'f- scale of the barometer, but nut for ermr in the length of the 



scale. 



I 



mam 

 rl>c(l. 



nF.TF.RMINATION OF PRESSURE OF IIYDROliF.N FOR COMPARISON WITH PRESSURE <1F OXVC,l.N. 



Fel)ruary r, 3 1>.M 7.^6.48 mm. 



,5.40 P.M 736-50 '"'"• 



4.10 p.M 736.51 mm. 



4.:?o I'.M 736.5' "ini- 



8 p.M 736.49 '"'"• 



8 10 p.M 73645 '"'"■ 



February 2, 10 a.m 736-47 '"'"- 



Mean 736-49 mm. 



