1901.] on Gases at the Beginning and End of the Century. 735 



The following table of the names of investigators who have con- 

 tributed to the experimental, theoretical, or practical study of gases 

 at once suggests much deserving work that otherwise ought to have 

 been discussed had time permitted. All we can do is to make in 

 rapid succession the fundamental experiments illustrative of the 

 great advances made during the century. [Experiments here.] 



Table of Investigators. 



Dalton, Gay Lussac, Faraday, Davy, Avogadro, Caignard de la 

 Tour, Regnault, Magnus, Thilorier, Natterer, Deville, Graham, 

 Joule, Kelvin, Andrews, Herepath, Wollaston, Clausius, Rankine, 

 Maxwell, Boltzmann, Stoney, Tait, Van der Waals, Mendeleef, 

 Amagat, Rayleigh, Crookes, Pictet, Cailletet, Wroblewski, Olszewski, 

 Kundt, Warburg, Witkowski, Onnes, Young, Eamsay, Leduc, Mathias, 

 Siemens, Kirk, Coleman, Liude, etc. etc. 



It is unnecessary to enter into any detailed discussion of the pro- 

 gress made since liquid air came to be an instrument of scientific 

 research, as this has been done in previous Friday Evening Dis- 

 courses ; but recent improvements in apparatus and methods of 

 manipulation may be worthy of consideration. The facility and 

 ease of handling, storing and working with liquid gases is de- 

 pendent on the use of vacuum vessels, many types of which may 

 be seen in Diagram 1. 



Fig. 8 of the diagram is a copy of the highly exhausted calori- 

 meter used in 1875 in a research 'On the Physical Constants 

 of Hydrogenium,' * and which for all intents and purposes was a 

 vacuum vessel made of brass instead of glass. The use of such an 

 arrangement to guard against gain or loss of heat was a natural 

 deduction from the early work of Dulong and Petit on radiation. 

 Many convenient forms may be given to such vessels, and several 

 varieties are represented in the diagram. The types 3 and 9, con- 

 taining a spiral-tube arrangement to relieve the contraction when 

 the inner vessel has to be joined to the outer by a tube, are of special 

 importance when regenerative methods have to be employed, because, 

 while isolating the metallic coil, it allows the liquid gas as it is formed 

 to drain away from the interior, and be collected in another vacuum 

 vessel outside of the main apparatus. This device, developed after 

 many unsuccessful attempts to construct such a vacuum vessel, was 

 found to-be essential for the easy production and collection of liquid 

 hydrogen, and as all the Eoyal Institution designs for such special 

 vessels have been made in Germany, they have been supplied to and 

 utilised by other workers, unconscious, it may be, where or how they 

 originated. Such vessels may be silvered in whole or in part, or 

 the vacuum may be nothing but mercury vapour. When liquid 

 hydrogen has to be kept naturally, the vacuum vessel in which it is 

 collected is placed in another vessel full of liquid air, so that the 

 external wall of the hydrogen vacuum vessel is kept at about — 190° C, 



* Trans. Royal Society of Edin. vol. xxvii. 



