498 Chronicles of Science. | July, 
sponding to a higher degree of incandescence. The second spectrum 
is produced by a very much more intense heat than that required to 
show the two first spectra. Oxygen, chlorine, bromine, and iodine 
have only one spectrum. 
Mitscherlich has found that when a drop of a solution of chloride 
of barium mixed with sal ammoniac is introduced.into the flame of a 
spectroscope, two brilliant green rays, having no connection with the 
barium spectrum, make their appearance. Sometimes these two green 
rays are unaccompanied by the barium spectrum, and sometimes they 
are superimposed upon it. He also finds that most metallic spectra 
are modified by the presence of hydrochloric acid, or chloride of am- 
monium vapour; in some the lines entirely disappear, while in others 
new lines make their appearance. He explains this by assuming that 
in the one case the spectrum is that of the metal itself, whilst in the 
other it is that of the compound. 
The spectrum of carbon has attracted considerable attention lately. 
From an examination of the spectra produced by carbonic oxide, car- 
bonic acid, sulphide of carbon, cyanogen, and olefiant gas, either ignited 
in the air or rendered incandescent by the spark of an induction coil, 
Dr. Attfield was led to the conclusion that certain lines which were 
common to all of these compounds were due to carbon, and constituted 
the spectrum of this element. M. Morren, in examining a candle 
flame, finds that the blue portion at the base of the flame “is the 
vapour of carbon preserved from combustion, but kept at a very high 
temperature by the envelope of hydrogen,” M. Morren leaves us in 
the dark as to how the carbon gets into this vaporous state, neither 
does he explain how it is that the low temperature of the blue part of 
the candle flame is hot enough to keep free carbon ina state of vapour, 
when it is notorious that the highest artificial heat yet produced is in- 
sufficient to effect this. According to Dr. Roscoe, the spectra which 
these various forms of carbon compounds give when in the state of 
incandescent gas are not quite identical. Thus, the so-called carbon 
rays obtained with the flame of olefiant gas differ from those ob- 
tained by the electric discharge through a vacuum of the same gas; 
whilst a spark passing through a cyanogen vacuum produces a spec- 
trum identical with that of the olefiant gas flame, and the spark 
through a carbonic oxide vacuum gives a spectrum coincident with 
that of the olefiant gas vacuum. 
A series of experiments on the intensity of the solar radiation has 
been made by Father Secchi; his apparatus consists of two cylinders 
placed one within the other, the space between the two being filled 
with water at a certain temperature. The aperture of the inner cylin- 
der is closed at one end by a plate of glass, and the other is partially 
closed by a diaphragm with an aperture ; a black bulb thermometer is 
placed in the axis of the inner cylinder. On exposing this instrument 
to the sun, it was found that the same difference of temperature between 
the black bulb thermometer was always maintained. whatever was the 
temperature of the water, and that the sun at mid-day produced no 
