50 Notices respecting New Booh. 



other, of considerable height, was intended to contain columns of 

 mercury making equilibrium at pressures carried as high as thirty 

 atmospheres. Nothing can be more interesting to read, to persons 

 who have to perform the manipulations necessary in experimental 

 researches, than the details of the ingenious and simple means by 

 which M. Regnault succeeded in cementing into the tubulures and 

 connecting end to end, the different tubes of the apparatus. 



The plan by which he contrived to effect this union, is of such 

 convenient and sure application, that its employment will doubt- 

 less become general, especially on account of the facility with which 

 it allows of the instantaneous mounting and dismounting of the dif- 

 ferent parts of the manometer, without risk of accident. We can- 

 not, to our great regret, dwell upon these details, which would lead 

 us too far, any more than upon the precautions necessary for the 

 exact measurement,* with the cathetometer, of the difference of level 

 between the surface of the column of mercury which rises in the 

 little tube containing the compressed air, and the surface of the 

 column of mercury raised in the large open tube, communicating of 

 course with the atmosphere. One point of some importance, is to 

 take into account the difference of height, and consequently of the 

 atmospheric pressure, due to the elevation of the second of the mer- 

 curial surfaces above the level of the mercury in the reservoir ; M. 

 Regnault found, by direct observation, that this element of correction 

 could not be neglected any more than that relating to the increase 

 of the capacity of the tubes under the influence of the high pres- 

 sures to which they were subjected. Finally, it is necessary to wait, 

 before making an observation, till the heat liberated in the gas in 

 consequence of the compression has been dissipated, and to employ 

 a current of water to maintain it, during the experiment, at a tem- 

 perature as constant as possible. 



The gases on which M. Regnault's experiments were made, are 

 atmospheric air, nitrogen, carbonic acid and hydrogen ; there were 

 several different series of experiments made on each gas, from the 

 ordinary atmospheric pressure up to the pressure of nearly thirty 

 atmospheres, expressed by columns of mercury of about twenty-two 

 metres in height. 



The detailed tables of the experiments contain all the numerical 



(r) 



data which permit the calculation of the relation ■- -, a relation 



(pi)' 



which would be equal to 1, if Mariotte's law, that the volumes are in 

 inverse proportion to the pressures, were correct. Now it is seen 

 that atmospheric air does not follow this law strictly, and that it 

 really becomes a little more compressed than it should according to 

 that law. It might be feared perhaps that the difficulty of exactly 

 appreciating the volumes Vq and Vj was the cause of the result con- 

 trary to Mariotte's law ; but supposing that this circumstance gave 

 rise to an error in the case of a certain pressure, the error ought to 

 be always the same for all pressures. 



