perpendicular to each other. In some of these ways the lines due to dust
might either be avoided or so much reduced in length as not to resemble
the true lines of the spectrum.

The 15 inch refractor is now being used with a modification of the
apparatus employed by Dr. Draper in his first experiments--a slit
spectroscope from which the slit has been removed. A concave lens has
been substituted for the collimator and slit, and besides other
advantages, a great saving in length is secured by this change. It is
proposed to apply this method to the 28 inch reflector, thus utilizing
its great power of gathering light.

[A description of an accompanying plate here follows, which is omitted,
as the plate cannot be easily reproduced for ordinary press printing.]

The results to be derived from the large number of photographs already
obtained can only be stated after a long series of measurements and a
careful reduction and discussion of them. An inspection of the plates,
however, shows some points of interest. A photograph of _a Cygni_, taken
November, 26, 1886, shows that the H line is double, its two components
having a difference in wave length of about one ten-millionth of a
millimeter. A photograph of _o Ceti_ shows that the lines G and _h_ are
bright, as are also four of the ultra-violet lines characteristic of
spectra of the first type. The H and K lines in this spectrum are dark,
showing that they probably do not belong to that series of lines. The
star near _[chi]' Orionis_, discovered by Gore, in December, 1885, gives
a similar spectrum, which affords additional evidence that it is a
variable of the same class as _o Ceti_. Spectra of _Sirius_ show a large
number of faint lines besides the well-known broad lines.