[ 239 ] 

 XXVI. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 153.] 

 January 23, 1868. — Dr. William B. Carpenter, Vice-President, in 



the Chair. 



THE following communication was read : — 

 u Description of a Hand Spectrum-Telescope." By William 

 Huggins, F.R.S. 



The instrument described in this paper was contrived in the sum- 

 mer of 1866, for the purpose of observing the spectra of meteors and 

 their trains. The special suitability of this apparatus, as a hand- 

 spectroscope, for the examination of the spectra of the lights which 

 may be seen about the sun during the total solar eclipse of next year, 

 induces me to offer a description of it to the Royal Society. 



The apparatus consists essentially of a direct-vision prism placed 

 in front of a small achromatic telescope. 



fc= kfria, _ »- - - , - 



The achromatic object-glass, marked a, is 1*2 inch in diameter, 

 and has a focal length of about 10 inches. The eyepiece (b) con- 

 sists of two plano-convex lenses. As a large field of view is of great 

 importance, especially for its use as a meteor-spectroscope, the field- 

 lens is made of nearly the same diameter as the object-glass. The 

 imperfect definition at the margin of the field is not of much practi- 

 cal importance, as the spectra can he brought for examination into 

 the centre of the field. The field-lens is fixed in a sliding tube, 

 which permits the distance between the two lenses of the eyepiece 

 to be altered ; in this way the magnifying-power of the instrument 

 may be varied within certain limits at pleasure. Before the object- 

 glass is fixed a direct -vision prism (c), consisting of one prism of 

 dense flint glass, and two prisms of crown glass. 



The field of view of my apparatus embraces an area of sky of about 

 7° in diameter. The spectrum of a bright star has an apparent 

 length of nearly 3°. The spectrum of the Great Nebula in Orion 

 appears as two bright lines, one of them broad, crossed by a faint 

 continuous spectrum. The magnifying-power of the telescope is in- 

 sufficient to show the three distinct lines of which the spectrum of 

 the nebula consists. The continuous spectrum is due to the stars 

 of the trapezium, and the other fainter stars scattered over the 

 nebula. 



For the purpose of testing the efficiency of this instrument as 

 a meteor-spectroscope, I observed the spectra of fireworks seen from 

 a distance of about three miles. The bright lines of the metals con- 

 tained in the fireworks were seen with great distinctness. I was able 

 to recognize sodium, magnesium, strontium, copper, and some other 

 metals. 



