LIGHT, LUMINARIES AND LIFE. 215 
Mr. Tuckwell has, however, committed himself to a definite piece 
of “criticism,” in which he questions my physics. He might have 
been, I think, a little more cautious. He says there is a little con- 
fusion of thought concerning the presence of steam, in what I have 
for the last twenty years or more spoken of as the “ pre-oceanic 
stage” of planetary development. There is some ‘confusion of 
thought,” but the confusion is Mr. Tuckwell’s. He has confounded 
two physical facts, which are entirely distinct, when he makes the 
critical temperature of steam to mean the temperature of dissoci- 
ation. The critical temperature of steam is that temperature above 
which no pressure can coerce it into a liquid ; and that, as he says, 
is about 773° Fahr., or a little above 400° C., about the melting- 
point of zinc. But the steam remains a true dry gas of the 
molecular composition H,O, as every student of physics knows. 
The temperature of the dissociation of steam is far higher. Under 
ordinary atmospheric pressure, the dissociation of steam is known 
experimentally to begin at about the temperature of white-hot 
platinum; but the temperature of complete dissociation is far 
above the melting-point of platinum, which is about 2,000° C. 
(=3,632° Fahr.) This is known from the fact that platinum 
melts readily in the flame of the oxy-hydrogen blowpipe, in which 
hydrogen and oxygen are entering into combination at a temperature 
which of necessity is below the temperature of complete dissociation 
of H,O. I have often demonstrated this in former years in lectures 
to my pupils. Perhaps the best account of “ dissociation,” which 
occurs to me, is that given in the Introduction to Professor 
Wislicenus’s Lehrbuch der Anorganischen Chemie. He might also 
possibly find of some interest my two papers on “ Dissociation,” read 
before the British Association in 1886 and 1888, and published in 
eatenso in the Chenical News. The electrolytic decomposition of 
H,0 into oxy-hydrogen gas is of course a different matter. 
“Sons of God.” Without attempting any definition of “ inspira- 
tion,” though insisting upon revelation coming to mankind through 
an “inspired race,” leading up to the greater Pentecostal Illumination 
of the Church,* we may reason inductively from the use of this 
expression in the Bible ; and it is only fair to claim that the fuller 
” 
* Professor Masterman’s little work, J believe in the Holy (Ghost, is 
useful in this connection (Wells Gardner & Co., 1906). 
P 
