LECTURES. 43 
of fine platinum wire, enclosed in a flask, was alternately caused to 
become white hot and cold, by intermittent passing an electric 
current through it. The arrangement was automatic. The expans- 
ion of the air in the flask produced by the hot wire cause the surface 
of a column of mercury in a U tube connected with the flask to 
become lowered, and this lowering caused the current heating the 
wire to cease. The heat occurred ata moment favourable for the 
maintenance cf the vibrations of the mercury column. He passed 
on next to consider Rijke’s notes. The glass tube he held contained 
at an inch or two from the bottom a piece of iron wire gauze. He 
now heated the gauze to a red heat by holding it over the blow-pipe 
flame and quickly removed the blow-pipe. Whilst cooling, the tube 
gave forth a note lasting for a few seconds. The explanations of 
these notes was similar to that of the sounding flames. The sound 
developed in a large tube was very striking. He had there a drain 
pipe six feet long and four inches in diameter. At abouta foot from 
the lower end a double thickness of wire gauze was inserted. On 
heating this gauze to a red heat, and removing the lamp, a very 
powerful note is produced. The notes thus produced lasted only 
for a short time. By the device of using a piece of platinum wire 
gauze instead of iron wire, and holding the gauze, after being heated, 
over an unlighted Bunsen burner, the sounds might be made con- 
tinuous. This was effected by taking advantage of the property 
possessed by clean platinum of becoming red hot when exposed to 
a mixture of air and coal gas, which property it owes to its causing 
a slow combustion of the mixed gases in contact with it. 
He would now shew another way of causing flames to produce 
a sound in a tube, and by way of distinction he would call these 
shrieking flames; as the sounds produced were both louder and 
harsher than those given by the hydrogen jet. Into the middle of 
a glass tube was put a piece of iron wire gauze ; the tube was then 
held over the mixture of air and gas issuing from an unlighted 
Bunsen burner, and the gas issuing from the top of the glass tube 
lighted. The flame at first remained on the top of the tube; but 
by carefully lowering the gas, the flame passed down the tube until 
it met the wire gaze, when it was arrested and gave rise to a loud 
note. 
The lecturer said he then came to the last division of his 
subject—Sensitive Flames. The. ames were very readily produced. 
All that was necessary was to have a supply of coal gas at a high 
pressure, and a burner made of a piece of quill glass tubing drawn 
