NovEmMBER 10, 1899. ] 
tube with the spectrum of hydrogen in the 
Orion Nebula, by methods devised by 
Messrs. Campbell and Wright, led to some 
interesting results, which have been pub- 
lished, with other spectroscopic papers, in 
the Astrophysical Journal. 
For the remaining half of the time the 
telescope has been used for micrometric 
work by Professor Hussey, Mr. Perrine and 
Mr. Aitken, and occasionally by other ob- 
servers. Series of observations of the satel- 
lites of Neptune and Mars have been made 
by Professor Hussey; of the satellites of 
Neptune and Uranus by Mr. Aitken. One 
hundred and fifty sets of measures of plane- 
tary nebulle, for parallax, and a set of 
measures for determining a possible refrac- 
tive effect on stars by the head of Swift’s 
comet, have been made by Mr. Perrine. 
The 36-inch telescope is also used for the 
observation of comets, and sometimes, par- 
ticularly in the case of expected comets, for 
purposes of discovery. Thus Wolf’s periodic 
comet was discovered by Professor Hussey, 
and Temple’s second periodic comet and 
Holmes’ periodic comet were discovered by 
Mr. Perrine, with this telescope. In the 
course of his cometary observations Mr. 
Perrine has found one close double star and 
about thirty new nebule. The formation 
of a second nucleus in the head of Swift’s 
comet was also discovered by him on May 
11th. 
Double stars are regularly observed with 
the 36-inch telescope, but they will be con- 
sidered in connection with the smaller (12- 
inch) instrument. 
THE CROSSLEY THREE-FOOT REFLECTOR, 
After many experiments, changes and 
minor improvements, this telescope has 
been brought into excellent working order. 
It is in the personal charge of the Director, 
who is assisted by Mr. H. K. Palmer. It 
will be used for various astrophysical re- 
searches, and more particularly for the 
SCIENCE. 
667 
photography of nebule, for which purpose 
it has proved to be admirably efficient. 
Some of the improvements which have 
been made are as follows: The pier has 
been cut down two feet, greatly increasing 
the facility with which the instrument can 
be handled. A new and powerful driving- 
clock has been made by the Observatory 
instrument maker, from designs by Pro- 
fessor Hussey. The double-slide guiding 
apparatus and the slow motions have been 
repaired and improved, and electric illumi- 
nation provided for the former. Wires for 
electric lighting and for telephone communi- 
cation have been run to the main Observa- 
tory. The study and the photographic room 
have been fitted up in a convenient manner 
for work. A very rigid declination clamp 
has been added to the mounting. The 
observing slit in the dome has been fitted 
with an adjustable wind-screen, on the 
general plan of the one used at the Yerkes 
Observatory. 
The interior walls of the dome have been 
painted bright red; the inner surface of the 
dome itself, black. By means of a large 
red lamp on a movable stand, the interior 
is sufficiently lighted for the convenience 
of the observers, without danger of fogging 
the sensitive plate. These precautions are 
necessary, because the ‘tube’ of the Cross- 
ley reflector is merely a framework of iron 
rods, which does not exclude the light like 
the tube of an ordinary telescope. 
Observation with the Crossley reflector 
is subject to more limitations than observa- 
tion with the other instruments. Work 
cannot be pursued on moonlight nights, in 
slightly foggy, or even in damp weather. 
Nevertheless, about 70 photographs have 
been made of 40 different nebule and star- 
clusters, mostly with long exposures of from 
three to four hours each, and from the most 
interesting of these, positive enlargements 
have been made on glass. The definition 
of these photographs, and the amount of 
