105 



| Barker. 



The day of the eclipse was all that could be desired. The sky was 

 almost without a cloud throughout, and the dew point was found to be at 

 least 34° F. below the temperature of the air. The entire programme of 

 observations was carried out as it had been arranged, and with singularly 

 good fortune. "The results obtained," as summarized by Dr. Draper, 

 "were : 1st, the spectrum of the corona was photographed and shown to be 

 of the same character as that of the sun and not due to a special incan- 

 descent gas ; 2d, a fine photograph of the corona was obtained, extending 

 in some parts to a height of more than twenty minutes of arc, that is, of 

 more than 500,000 miles ; 3d, the Fraunhofer dark lines were observed by 

 both Professors Barker and Morton in the corona ; 4th, the polarization 

 was shown by Professor Morton to be such as would answer to reflected 

 solar light ; and 5th, Mr. Edison found that the heat of the corona was 

 sufficient to send the index beam of light entirely off the scale of the gal- 

 vanometer. ' ' As these results seem to be of very considerable importance, 

 it appears desirable to give the various methods of observation somewhat 

 more in detail, adopting for the purpose so tar as possible the language of 

 the observers themselves, as given in their several reports. 



Photographic and Phototelespectroscopic Observations. 



Fis. 1. 



The instruments which were used 

 by Dr. Draper in his photographic 

 and phototelespectroscopic obser- 

 vations were : " 1st. An equatorial 

 mounting, with spring governor 

 driving clock, loaned by Professor 

 Pickering, Director of Harvard Ob- 

 servatory. 2d. A telescope of five 

 and a quarter inches aperture and 

 seventy-eight inches focal length, 

 furnished with a lens specially cor- 

 rected for photography, by Alvan 

 Clark & Sons. 3d. A quadruple 

 achromatic objective of six inches 

 aperture and twenty-one inches 

 focal length, loaned by Messrs. E. A 

 H. T. Anthony, of New York ; to 

 this lens was attached a Rutherford 

 diffraction grating nearly two inches 

 square, ruled on speculum metal. 

 This arrangement (Fig. 1.) with its 

 plate holders, etc., will be desig- 

 nated as a phototelespectroscope. 

 Besides these there was a grating 

 spectroscope, an eye slitless prism 



PROC. AMEK. PHILOS. SOC. XVIII. 102. N. PRINTED JAN. 25, 1879. 



