not followed exactly in the Crossley apparatus. The guiding eyepiece
slides freely when not held by a clamp. Pin-holes for preventing fogging
are unnecessary when red light is used.
[9] It so happens that the tension of the vertical thread is such that it
begins to slacken when the temperature falls to within about 2 deg. of the dew
point. The thread thus forms an excellent hygrometer, which is constantly
under the eye of the observer. When the thread becomes slack, it is time
to cover the mirrors.
[10] _Mon. Not. R. A. S._, =48=, 352.
[11] The following list includes all papers of interest:
"Photographic Observations of Comet I, 1898 (Brooks), made with the
Crossley Reflector of the Lick Observatory." A. J. No. 451, =19=, 151; see
also _Ap. J._, =8=, 287.
"The Small Bright Nebula near _Merope_," _Pub. A. S. P._, =10=, 245.
"On Some Photographs of the Great Nebula in _Orion_, taken by means of the
Less Refrangible Rays in its Spectrum," _Ap. J._, =9=, 133. See also _Pub.
A. S. P._, =11=, 70; _Ap. J._, =10=, 167; _A. N._, 3601.
"Small Nebulae discovered with the Crossley Reflector of the Lick
Observatory," _Mon. Not. R. A. S._, =59=, 537.
"The Ring Nebula in _Lyra_," _Ap. J._, =10=, 193.
"The Annular Nebula H. IV. 13 in _Cygnus_," _Ap. J._, =10=, 266; see also
_Pub. A. S. P._, =11=, 177.
"On the Predominance of Spiral Forms among the Nebulae," _A. N._, 3601.
"The Distribution of Stars in the Cluster _Messier 13_ in _Hercules_" (by
H. K. Palmer), _Ap. J._, =10=, 246.
"The Photographic Efficiency of the Crossley Reflector," _Pub. A. S. P._,
=11=, 199; _Observatory_, =22=, 437.
"New Nebulae discovered photographically with the Crossley Reflector of the
Lick Observatory," _Mon. Not. R. A. S._, =60=, 128.
"The Spiral Nebula, H. I., _55 Pegasi_," _Ap. J._, =11=, 1.
"Photographic Observations of Hind's Variable Nebula in _Taurus_, made
with the Crossley Reflector of the Lick Observatory," _Mon. Not. R. A.
S._, =60=, 424.
"Use of the Crossley Reflector for Photographic Measurements of Position,"
_Pub. A. S. P._, =12=, 73.
"Discovery and Photographic Observations of a New Asteroid 1899 FD.," _A.
N._, 3635.
"Elements of Asteroid 1899 FD." (by H. K. Palmer), _A. N._ 3635.
[12] Footnote added in 1908: This concluding paragraph, retained in the
present publication for completeness, loses point in some particulars,
because the photogravure referred to is not reproduced here. The
heliogravure reproduction of the Trifid nebula is No. 55.
[13] Since then a photograph by Dr. Roberts has appeared in _Knowledge_,
=23=, 35, February, 1900.
Transcriber's Notes:
Passages in italics are indicated by _italics_.
Passages in bold are indicated by =bold=.
Superscripted characters are indicated by ^x.
Subscripted characters are indicated by _{x}.
The original text utilizes a circle symbol; this is represented in this
text version as [circle].