288 On Physical Observations to be undertaken in India. [Mar. 5, 



*'If tliese objects are visible by reflecting to us the light of the photo- 

 sphere, their spectra would be identical, or nearly so, with the normal solar 

 spectrum. If, however, either the * corona' or the * red flames' are self- 

 luminouSj a supposition which appears not improbable in the case of the 

 red flames, some information as to their constitution may be expected to 

 be given to us by the prism. 



" § II. Description of Instruments sent out hy the Royal Society. 



^' The telescope provided for the spectrum-observations has an object- 

 glass of five inches aperture. The telescope is mounted on a portable 

 equatorial stand, with circles for declination and R. A., divided on silver. 

 The stand can be adjusted to any latitude ; and the whole instrument packs 

 into three boxes for convenience in travelling. 



"The telescope has a very perfect driving-clock, the rate of which is 

 maintained uniform by means of a form of pendulum governor recently in- 

 vented by Mr. Cooke, by whom the whole instrument has been specially 

 constructed for these observations. A Barlow lens is fitted to the tele- 

 scope for the purpose of increasing the size of the image formed by the 

 object-glass. The finder is wired in a special manner, and has a diagonal 

 eyepiece for convenience in looking from it to the small telescope of the 

 spectrum-apparatus attached to the equatorial telescope. 



*' The spectroscope, constructed by Messrs. Simms, has one prism of 

 dense flint glass, with a reflecting angle of 60°. The instrument is fur- 

 nished with a micrometer-screw for measuring the position in the spectrum 

 of any lines observed. There is also provided a photographed scale 

 illuminated by a small lamp, which can be seen by reflection from the 

 second surface of the prism. The positions of lines in the spectra observed 

 can be read by means of the reflected image of the divisions of this scale. 



" The slit of the instrument is so constructed that both jaws open 

 equally. A cylindrical lens is provided for the observation of stellar 

 spectra. The instrument is furnished with a prism and mirror, by means 

 of which the spectra of terrestrial flames can be compared directly with 

 the spectra of the objects to which the telescope is directed. 



"Four portable hand spectrum-telescopes are provided, by means of 

 which it will be possible to determine the general character of the spectra 

 of the lights seen about the sun at the time of the eclipse. 



*' For the purpose of analyzing 'the light of the * corona ' and ' red 

 flames' for polarization, a second telescope has been procured, of three 

 inches aperture. This instrument has altitude and azimuth motions on a 

 portable tripod stand. It is furnished with three eyepieces, magnifying 27, 

 41, and 98 diameters. By a suitable arrangement of adapters, either of 

 the following analyzers can instantly be used either in connexion with eye- 

 piece 27 diameters or eyepiece 41 diameters. 



" The first analyzer consists of a double-image prism, and a plate of 

 quartz cut perpendicularly to the axis. When polarized light is present 



