Intelligence and Miscellaneous Articles. 237 



The reservoir with parallel glass plates is that of the Scientific 

 Association of France, which one of us had constructed for another 

 research at the Paris Observatory, made under the auspices of M. 

 Le Verrier. It consists essentially of a horizontal copper cylinder, 

 of a capacity of about 7 litres, with glass plates at its extremities, 

 and heated by an oil bath. To this cyclinder we fitted a large stop- 

 cock, of 4 square centimetres aperture, for the escape of the steam. 

 The duration of the flow was so small that the heating-action of the 

 sides during the expansion could be neglected. To this apparatus 

 we connected a steam-boiler, of a capacity of ISO litres, so large 

 that it was easy to maintain a constant pressure, and, lastly, a 

 manometer arranged so that all the measurements were accurate. 

 The experiments were made last September, in the manufactory of 

 Haussman, Jordan, Hirn, and Co., at Logelbach, near Colmar. 



The oil bath being at a given temperature, and the water in the 

 boiler at a lower one, a quantity of vapour was driven through the 

 cylinder sufficient to expel all the air. The escape stopcock was 

 closed, the pressure kept constant, and the tube from the boiler to 

 the cylinder heated so that the vapour of the latter was well dried. 

 Both the pressure and the temperature of the oil bath were noted. 

 Closing the communication, and opening the large stopcock, a 

 screen of paper brightly illuminated, or a mirror reflecting the day- 

 light, was looked at through the glass plates. The experiment was 

 repeated at the same temperature, but with different initial pressures. 

 Supposing that we start from a pretty strong pressure, we observe a 

 thick mist. Working then at decreasing pressures, the mist 

 diminishes, passes through a series of stages, and ultimately appears 

 no more ; the limit sought has then been exceeded. Increasing 

 the pressure, the mist is again found ; and by repeating the observa- 

 tions under pressures alternately increasing and decreasing, we can 

 ultimately estimate the original pressure corresponding to the limit 

 sought with an absolute error of -^ of an atmosphere. 



We give in a Table the results of ten series of observations ; the 

 temperature is given by the air-thermometer : — 



Initial 



Initial 



Final 



Final 



pressure. 



temperature. 



pressure. 



temperature. 



atm. 



o 



atm. 



6 



1-597 



131-5 



0-984 



99-6 



1-685 



151-8 



0-984 



99-6 



2-115 



174-0 



0-981 



99-5 



2-219 



179-0 



0-981 



99-5 



2-451 



189-2 



0-979 



99-4 



2-528 



192-2 



0-981 



99-5 



2-636 



197-8 



0-975 



99-3 



3-231 



219-4 



0-975 



99-3 



3743 



2390 



0-967 



99-1 



4-275 



254-7 



0-967 



99-1 



From our experiments, the law of the expansion of superheated 

 steam cannot be represented by the known formula of Laplace and 



