SCIENTIFIC SUMMARY. 
577 
prepared surface, there is no indication of the activity of the chemical 
rays suffering any diminution, but, on the contrary, at these altitudes they 
are not so liable to b affected or absorbed by transmission through dense 
air and other media. A further illustration of this fact may be gathered 
from the statements published many years ago by Mr. Crookes, to the 
effect that the prismatic spectrum was of greater length and purity, and 
that the more refrangible solar rays were better defined optically, and 
endowed with greater photographic activity, at noon on a fine Midsummer 
day than at any other season of the year ; this result being the necessary 
consequence of their more perpendicular passage at this time through the 
earth’s atmosphere. If now the experimental observations of Mr. Glaisher 
be considered in connection with the well-known fact that photographic 
papers lose much of their sensitiveness when deprived, by the action of 
heat or desiccating substances, of the greater part of their hygroscopic 
moisture, the interesting announcement of that gentleman may be regarded 
as furnishing from external nature a confirmatory illustration of this 
truth, and not be evidence of a notable diminution in the chemical activity 
of the sun’s rays at these great altitudes. 
PHYSICS. 
D R. W. A. MILLER has been examining the spectrum of thallium, 
under the influence of a progressively-increasing temperature. It 
is well known that when thallium is examined in the ordinary way it 
exhibits in the spectroscope only a single green line of intense brightness. 
Dr. Miller found that on employing the flame of burning hydrogen, and 
then of the oxyhydrogen jet, as the temperature increased the brilliancy of 
the green line also increased, but no new lines made their appearance ; but 
on employing two stout thallium wires as the electrodes of a strong 
induction coil, by which means a still higher degree of heat was obtained, 
several new lines which were proved to belong to the metal appeared. In 
addition to the intense green line, the spectrum contains several very 
characteristic groups of lines, somewhat similar to those of the spectra of 
cadmium and zinc, and in a less degree like that of lead. 
MM. P. Christofle and F. Beilstein have been examining the spectrum of 
phosphorus and the coloration of the hydrogen flame by phosphorus and its 
compounds. A very small quantity of phosphorous acid communicates a 
beautiful green colour to the hydrogen flame. On examining by means of a 
spectroscope the flame of hydrogen into which either this substance, phos- 
phorus, or hypo-phosphorous acid was introduced, two beautiful green lines, 
and a third a little less vivid, appeared. From the extreme sensibility of 
this method, and the exact results obtained, it is evident that the process 
may be used for detecting phosphorus in cases of poisoning. 
Mr. Gassiot exhibited, at a recent soiree of the Royal Society, a very 
powerful spectroscope, with nine glass prisms. It showed the yellow 
sodium line double, the two portions appearing about a quarter of an inch 
asunder. 
