Barker.] lIO [Nov. 15, 



ical spectroscope by Merz of Munich; (3) a second direct vision spectro- 

 scope by Hoffmann of Paris ; and (4) a pocket spectroscope by Geo. Wale & 

 Co. Beside this spectroscopic outfit, a second four inch achromatic tele- 

 scope by Dollond was taken for use with the tasimeter by Dr. Edison, and 

 a Savart, a Scnarmont, and an Arago polariscope, for determining the 

 polarization of the corona. The Merz spectroscope above mentioned is 

 described in the "Philosophical Magazine," IV., xli., Feb., 1871. It is 

 provided with two compound direct vision prisms, of which one or both can 

 be used at pleasure, each consisting of rive single prisms, two of flint glass 

 with a refracting angle of 84°, and three of crown ; one of these having a 

 refracting angle of 84°, the others of 87°. The dispersive power of each 

 of these compound prisms is about equal to that of two equilateral prisms 

 of flint glass. The instrument has a collimating and an observing tele- 

 scope, each furnished with an object glass two-thirds of an inch in aper- 

 ture and four inches in focal length. The prism-tube is attached to the 

 collimator by two centres, giving it a lateral motion about a line passing 

 through these centres, which constitutes an axis parallel to the slit. The 

 observing telescope is similarly attached to the tube carrying the prism. 

 These motions serve to alter the incidence of the rays upon the surface of 

 the prism, and also to bring any special part of the spectrum into the mid- 

 dle of the field. The observing telescope is provided with a positive eye- 

 piece of an equivalent focal length of one inch, and also with a needle 

 micrometer, having an eye-piece of one-half inch focus. The graduations 

 upon this micrometer are strongly cut, enabling the positions and the dis- 

 tances of the lines measured with it to be easily read even in a faint light. 

 The spectroscope was firmly attached to the draw tube of the equatorial 

 telescope bj^ means of an open frame made by Zentmayer, so that the posi- 

 tion of the image with reference to the slit could be readily observed. 



The time from the date of our arrival at Rawlins until the eclipse, was 

 occupied in setting up the instruments, in getting them into adjustment, 

 and in practice with them. It was found that with only one of the com- 

 pound prisms of the Merz spectroscope, the slit being placed radially, it 

 was easy to observe the lines C and F reversed in the chromosphere, and 

 also the bright line D 3 . On the morning of the day of the eclipse, the 

 solar edge was examined for protuberances, in order to locate them in ad- 

 vance of totality. But a single one was noticed, this being on the south- 

 western edge of the sun. As the time of first contact approached, the 

 spectroscope was removed and a paper screen was attached to the draw- 

 tube, an image of the sun being formed on this screen by means of the 

 eye-piece ; thus enabling the time of this contact to be approximately de- 

 termined and the subsequent progress of the eclipse to be conveniently 

 observed. No spots were seen under these circumstances, though this 

 could hardly have been expected since the solar image was so small, 

 scarcely three inches in diameter, unless the spots were of large size. As 

 the time of second contact drew near, the spectroscope was replaced upon 

 the equatorial. Since you deemed it of importance to pay special attention 

 to the oxygen lines in the vicinity of G, the micrometer of this instrument 



