the elements have few strong lines or none at all in the limit of the
solar spectrum when the arc spectrum, which I have used, is employed.
Thus, boron has only two strong lines at 2497. Again, the lines of
bismuth are all compound, and so too diffuse to appear in the solar
spectrum. Indeed, some good reason generally appears for their absence
from the solar spectrum. Of course, there is but little evidence of
their absence from the sun itself; were the whole earth heated to the
temperature of the sun, its spectrum would probably resemble that of the
sun very closely."

The powerful instrument used at Baltimore for photographing spectra, and
the measuring engine constructed to fit the photographs so that its
readings give the wave lengths of lines directly within 1/100 of a
division on Angström's scale, give the foregoing results a weight
superior to many others published.

* * * * *




ALLOTROPIC FORMS OF METALS.


Writing on some curious properties of metals and alloys, Mr. W.C.
Roberts-Austen, says the _Engineer_, remarks that the importance of the
isomeric and allotropic states has been much neglected in the case of
metals. Joule and Lyon Playfair showed, in 1846, that metals in
different allotropic states possess different atomic volumes, and
Matthiessen, in 1860, was led to the view that in certain cases where