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SCIENCE PROGRESS 



of observers have determined directly densities with reference 

 to oxygen. The results are set out below, together with the 

 mean values that have been adopted here : 



Rayleigh's figure for hydrogen has been omitted, as that 

 observer has recognised that it is too high, whilst Morley's 

 value of the density of oxygen has been used in calculating 

 Guye's results, since the value obtained for oxygen in Guye's 

 laboratory was recognised to be unsatisfactory. The mean 

 values have been converted into absolute densities by adopting 

 Morley's value of the absolute density of oxygen. As regards 

 the other figures in Table I., the value of L for ammonia is 

 the mean of those due to Guye and Pintza and Perman and 

 Davies and that for hydrogen chloride is the result obtained 

 by Gray and Burt ; the remaining values are those obtained in 

 Guye's laboratory (14, 16, 17, 19, 23, 24). 



