322 Intelligence and Miscellaneous Articles. 



The author gave a list of these fossils, and also of those of the Red 

 Chalk, the latter amounting to sixty-one, and presenting a mixture 

 of forms belonging to the Lower Chalk, Upper Greensand, and 

 Gault. On comparison with the Gault section at Folkestone, the 

 author considered it evident that the Red Chalk of Hunstanton was 

 equivalent to the upper part of that formation. He mentioned that 

 ten miles south of Hunstanton, in artificial sections, blue gault has 

 been found resting upon the Carstone, whilst rather nearer to 

 Hunstanton the same place was occupied by a red clay, connecting 

 the two dissimilar deposits, which, however, were shown by analysis 

 to contain nearly equal quantities of iron. If the Upper Greensand 

 be represented in the Hunstanton section, the author considered that 

 its place must be in the band numbered 2, containing Sijohonia para- 

 doxica and Avicida gryphceoides. 



XXXVIII. Intelligence and Miscellaneous Articles. 



ON THE EXPANSION OF GASES. 

 NOTE BY M. A. CAZTN, PRESENTED BY M. LEVERRIER. 



TN 1862* I gave an experimental method for making known the re- 

 -"- lation that exists between the pressure and the specific weight of 

 a gaseous mass when it expands without losing or receiving heat. 

 At that time I had applied this method between limits of pressure 

 only slightly differing from one another, not having the requisite ap- 

 paratus. I have now been able to work up to a pressure of 9 atmo- 

 spheres ; and it is the result of these new experiments that I have the 

 honour to communicate to the Academy. 



The apparatus is set up in a hall of the observatory. I owe a part 

 of the materials of it to the Scientific Association of France, and to 

 the generosity of M. Hugon. One of his gas-engines worked a 

 compression-pump ; and I cannot praise too highly its excellent ser- 

 vice. Let me be allowed here to thank MM. Leverrier and Hugon 

 for their kind assistance. 



I will now sketch out the principle of my method. The gas is 

 enclosed in two reservoirs, A and B, connected by a stopcock of 

 large orifice (4 centims. diameter). This stopcock being closed, a 

 pump withdraws the gas in the reservoir B and compresses it to the 

 pressure p x in the reservoir A. Let us suppose that we open the stop- 

 cock and close it again at the precise moment when there is an equa- 

 lity of pressure on both sides of the orifice. During the flow there 

 has been a cooling in A ; then, after closing, the sides have reco- 

 vered their initial temperature. The final pressure^ is measured ; 

 afterwards the stopcock is opened again, the equilibrium is allowed 

 to be reestablished, and the pressure/?., is measured. When the re- 

 servoir B is sufficiently large, this pressure does not differ appreciably 

 from the pressure acquired by the gas at the end of the expansion. 

 I observed this fact in pursuing a method which I have explained 

 in a preceding communication (March 9, 1868). The gaseous mass, 

 then, which remains in the reservoir A has passed rapidly from the 

 pressure p x to the pressure /?.,, and its specific gravity has passed 

 * Annales de Chimie et de Physique. 



