542 



Intelligence and Miscellaneous Articles. 



Limits of pressures, 

 in atmospheres. 



Air. 



Nitrogen. 



Oxygen. 



Hydrogen. 



Between 750 and 1000 

 1000 „ 1500 

 1500 „ 2000 

 2000 „ 2500 

 2500 „ 3000 



0000411 

 0-000268 

 0-000167 

 0-000123 

 0-000093 



0-000407 

 0-000265 

 0-000170 

 0-000122 

 0-000091 



0-000258 

 0-000160 

 0-000115 

 0-000091 



0000408 

 0-000272 

 0000197 

 0000158 



It will thus be seen that at very high pressures oxygen, nitrogen, 

 and air have almost the same compressibility ; it is of the same order 

 of magnitude as that of liquids ; at 3000 atm., it is virtually equal 

 to that of alcohol under the normal pressure. 



The compressibility of hydrogen is far greater, almost double ; 

 at 3000 atm., it is almost equal to that of ether towards the normal 

 pressure. 



It is easy to foresee that these compressibilities, like those of 

 liquids, should increase with the temperature ; that is shown by the 

 following table with respect to hydrogen. 



Limits of pressures 

 in atmospheres. 



Coefficients. 



At 0°. 



At 15°-4. 



At47°'3. 



Between 1000 and 1500 

 1500 „ 2000 

 2000 „ 2500 

 2500 „ 3000 



o-ooo 



0000263 

 0-000196 

 0-000156 



0-000408 

 0-000272 

 0-000197 

 0-000158 



0000416 

 0-000280 

 0-000208 

 0-000158 



The apparent densities are easily deduced from the former 

 table ; assuming provisionally the number generally adopted for the 

 compressibility of glass, the following results are obtained at 

 3000 atm. 



Densities at 3000 atm. compared with water. 



Apparent. Real. 



Oxygen 1-0972 1-1054 



Air 0-8752 0-8817 



Nitrogen 0-8231 0-8293 



Hydrogen 0*0880 0-0887 



The curves obtained, as I have already done, by putting the pres- 

 sures on the axis of the abscissae, and the products pv on that of the 

 ordinates, are nearly straight lines, but presenting all a slight con- 

 cavity turned towards the axis of the abscissse ; I shall return to 

 this important point in reference to limiting volumes, when I have 

 determined the alteration in volume of the envelopes. — Gompte 

 rendus, Sept. 17, 1888. 



OBSERVATIONS ON BREWSTER'S NEUTRAL POINT. 

 BY MM. J. L. SORET AND C. SORET. 

 The neutral point of atmospheric polarization which is below 

 the sun, and which was discovered by Brewster, has been rarely 



