BY JAMES TOLSON, ESQ. 59 
Value of R. 
Cast and Sheet Iron, rusted ... eee Ne 6868 
Wood Sawdust, fine ... ee oe Bes "7215 
Building Stone, Plaster, Wood, Brick av "7358 
Sand, fine + is Ee a me "7400 
Calicoz} .. lea Ae x a ae “7461 
Woollen Stuffs, any colour ... eae nue a isee- 
Silk Stuffs, Oil Paint ... sae Sd Bs "7583 
Paper, any colour se age ee i "7700 
Lampblack _... ede ss Le Ae ‘8196 
Water ... oF re a aA a) wess3 
Ice Ait i bei Ka aS. Ae 55 
Oil bu ie bie bis ea 2s 1°4800 
eats’). 33 doe WES 
TRANSPARENCY OF ATMOSPHERIC AIR TO THE Rays oF 
Rapiant Heat.—‘‘Atmospheric air has the remarkable property of 
allowing radiant heat to pass through it without being sensibly 
heated thereby. In experimenting upon this property, Tyndall 
found that the more refined the method used, and the more 
delicate the apparatus with which he worked, the less noticeable 
was the absorption. We are therefore entitled to say that air is 
transparent to heat rays, and that heat can pass through a 
moderate thickness of air or gas without appreciable loss or heat- 
ing the air sensibly, so that in ordinary cases air and gases cannot 
be heated directly by radiant heat, but only by contact with heated 
bodies.’’—Box, op. cit. 
Tyndall, in his work on heat, writes in reference to the 
transparency of dry air to radiant heat :— 
‘* A joint of meat might be roasted before a fire, the air round 
the joint being cold as ice. The air on high mountains may be 
intensely cold while a burning sun is overhead; the solar rays 
which, striking the human skin are almost intolerable, are incom- 
petent to heat the air sensibly, and we have only to withdraw into 
the shade to feel the chill of the atmosphere. Immersion in the 
shadow of the ‘Dome de Gouté’ at once changed our feelings, 
for here the air was at freezing temperature. It was not, how- 
ever, sensibly colder than the air through which the sunbeams 
passed, and we suffered, not from the contact of hot air, but from 
radiant heat which reached us through an ice cold medium.” 
Dr. Hooker, in his ‘“ Himalayan Journal,’ as quoted by 
Tyndall, writes— 
‘At 10,000 feet, at 9 a.m., I saw the mercury rise to 132° Fahr., 
while the temperature of the shaded snow hard by was 22° Fahr. 
At 13,000 feet elevation the thermometer has stood at 98° in the 
