USE OF SPECTROSCOPE IN ASTRONOMICAL OBSERVATION. 145 
was contrived by Mr. Huggins for the purpose of observing the 
spectra of meteors and their trains. The achromatic object- 
glass a is an inch and one-fifth in diameter, and has a focal 
length of ten inches. The eye-piece h consists of two plano- 
convex lenses. The magnifying power of the eye-piece can be 
varied within certain limits by changing the distance between 
the two lenses. The apparatus is used without a slit, so that it 
is only applicable to objects like stars or meteors, or the thin 
cusps of the lunar crescent, which have no perceptible breadth. 
In observing the lunar cusps, their length must of course be 
brought at right angles to the direction in which the spectrum 
is formed, and similarly with meteor-trains. Fraunhofer’s 
lines have been seen by Mr. Huggins in the spectrum of the 
moon when a very narrow cresceut. He also saw the bright 
lines belonging to several metals, in the spectra of the Crystal 
Palace fireworks, three miles from the place of observation. 
The dark lines of the stellar spectra are well shown by means 
of this instrument ; but as the spectrum of a star is a bright 
line, it is well to give a small breadth to the spectrum by 
means of a cylindrical lens fitted in a little cap which slips over 
the eye-lens and is placed next to the eye.” The spectrum of 
the great nebula in Orion shows two bright lines when observed 
with this instrument ; so that here we have another instance 
of an instrument of small price which affords a satisfactory 
answer to a question which it had been found hopeless to attack 
by the largest telescopes man could construct. 
In the expeditions sent out to view the great eclipse of 
August 1868, four of these instruments, made by Mr. Browning’, 
were sent out by the Eoyal Society to India. 
The field of view of the hand-spectroscope has a diameter of 
about seven degrees, according to the arrangement exhibited in 
fig. 4. Mr. Browning has suggested arrangements — presented 
in fig. 8 — by which the observation of moving bodies, such as 
meteors, is rendered much easier, on account of the great in- 
crease in the field of view. In fig. 8, aa represents a direct- 
vision spectroscope, b a plano-convex cylindrical lens, c a 
double concave lens of much greater focal length. The line 
1, 2, 3, represents the path of a meteor, and the dotted lines 
from the points 1, 2, 3, are seen to be so acted upon by the 
lenses as to produce an almost stationary image. With this 
instrument Mr. Browning found it easy to obtain the spectra of 
balls shot from a Koman candle placed but a few yards from the 
instrument. Although the angular velocity of the balls was of 
course very great, the characteristic lines of baryta, strontia, 
&c., were clearly exhibited. 
Appliances such as these may, of course, be equally well 
adapted to the Herschel-Browning direct -vision spectroscope. 
