192 Miscellaneous Intelligence, 



compressing force. Boyle and Muschenbroek thought they saw 

 errors in this hivv, even when the force was not above 4 atmos- 

 pheres. Robison and Sulzer carried the force to 8 atmospheres, 

 and agreed in giving the same departure from the law, namely, 

 that when compressed eight times, instead of exerting a force 

 eight times that of the common air, it was only six times greater. 

 Oersted, on the contrary, found the law true to 8 atmospheres, 

 and even up to 60 atmospheres ; but his mode of experimenting 

 is not satisfactory to the French commissioners, though the results 

 were correct. 



In the preparation of the manometer the experiments were car- 

 ried to 27 atmospheres, and the law found to be correct. It was 

 intended to ascertain if it held good with other gases than air, 

 but the authorities forbade the use of the old church tower for this 

 purpose. 



There appears to have been much fear about steam at the pres- 

 sure of 24 or 25 atmospheres ; and, lest the boiler should ex- 

 plode, and blow up the old vaults, and even destroy neighbour- 

 ing buildings, it was determined to have it in the court-yard "of 

 the observatory, and make the experiments there. Ultimately, 

 therefore, the manometer was transferred, though with great 

 difficulty, and finally placed in proper communication with the 

 boiler. 



Some important precautions were now taken to ascertain the 

 temperature accurately. The first was to take account of the 

 cooling effect of the air on that part of the thermometer exterior 

 to the boiler ; this was done by retaining it constantly at the same 

 temperature. The next was to prevent alteration in the capacity 

 of the bulb, by allowing the vapour to press upon it. This was 

 effected by putting the thermometers into gun-barrels, made thin, 

 closed at one extremity, and filled Avith mercury ; these, when 

 fitted to the boiler, were made to descend, one to the bottom of 

 the boiler nearly, to give the temperature of the water ; the other 

 to within a few inches of the water, to give the temperature of 

 the vapour. 



The temperature and pressure were then experimentally ascer- 

 tained up to 24 atmospheres ; after which formula was sought for, 

 by which they could be extended to higher pressures, and the fol- 

 lowing one adopted : 



e= (1 + 0.7153 0' 

 e being the elasticity ; t the excess of temperature above 100° C, 

 taking for unitylOO^ of the centigrade thermometer. This formula 

 nearly represents the results given by experiment up to 24 atmos- 

 pheres ; the greatest error has been at 8 atmospheres, and was 

 then 0.9 of a degree. It was more accurate for the higher pres- 

 sures, being calculated from them, and the commissioners have no 

 doubt that at 50 atmospheres the error is not more than 0,1 of a 

 degree. 



