682 On the Evidence that the Earth's Interior 1s Solid. (July, 
case of iron and lead by the assumption of a repulsive fore, 
much the same kind of explanation as “Nature abhorsa vac- 
uum,” for here the repulsion exists for iron but not for lead. He 
seems to have lost sight of the true problem before him: ls — 
solid metal at or near the melting point of a greater or less spe 
cific gravity than the same metal liquid at or near the point of — 
solidification, and substituted for it the question is cold solid — 
metal heavier or lighter than the same metal when heated to amy — 
temperature above the melting point. Surely the tendency of 
most bodies to expand on the application of heat would, in the 
case of iron and rocks, cause the difference between the cold solid _ 
and the liquid states, to be greater than it would be between the iy 
hot solid and the liquid states, a point that does not seem to have 
been properly appreciated in discussions of the earth’s strane , 
Mallet’s experiments show clearly that iron near the point of : 
fusion is lighter than the same when melted, but that lead is 
heavier. He calls attention to one very important pail , 
owing to the difference in specific gravity in the various grades | 
liquid and 
| 
cast-iron, it is necessary that in these experiments the ; 
solid should be of the same quality, otherwise real buoyancy : 
the reverse may occur from this cause. Mallet further yee i 
admit that liquid slag will allow solid slag to float upon pi 
on account of a certain vesicularity, whatever care may be taneh ; 
or on account of his hypothetical repellant force.’ igle : 
Some other experiments were made by Centner, W. a be : 
and Joseph Whitley.? The general result of these wo a 
show that cold steel, iron, brass and probably 
come lighter and will float ; also that lead p 
sess a higher specific gravity when solid, whether i 
than the molten metal. Lagi by Mal- 
In 1875 Mr. W. C. Roberts made some expeti i in the 
let’s method, on the density of silver in the cold wi oe 
molten condition. These showed that it was mol’ ee 
former than in the latter state.’ : at 
. Nature, We 
1 Proc. Roy. Soc., 1874, XXII, 366-368; 1875, XXIII, 209-234 
156, 157. a 
2 Nature, 1877, XV, 529, 530; XVI, 23, 24; 1878, paperei 39 as Mamul 
Whitley’s experiments are erroneously credited to Muir ee 
Geology, 1880, 3d ed., p. 810. 
8 Proc, Roy. Soc., 1875, XXIII, 349. 350, 481-495. 
