PHYSICS. 115 



the plate is proved. The oxygen lines in the air spectrum, 

 to the number of a dozen or more, coincide accurately with 

 bright solar lines, every peculiarity in the shading or group- 

 ing of the one being reproduced in the other. The demon- 

 stration is complete, and will materially modify existing 

 views as to the solar constitution. The discovery is the 

 most important made in solar physics since that of Kirch- 

 hoffin 1860. 



Youna: has made careful measurements of certain lines in 

 the solar spectrum, observed alternately upon the eastern 

 and western limbs of the sun, with a view to test the ques- 

 tion of the effect of the motion of a luminous body upon the 

 wave-length of the light which it emits. Using spectra of 

 the sixth and eighth orders produced by a Rutherfurd grat- 

 ing of 8640 lines, the overlapping spectra being separated 

 from each other by a glass prism of 45 placed between the 

 grating and the object-glass, with its refracting edge perpen- 

 dicular to the lines, the author succeeded in observing a dif- 

 ference in the position of the two D lines on the two edges, 

 which, admitting Doppler's theory, would give a velocity of 

 1.42 miles per second for a point on the sun's surface. As 

 direct observation gives but 1.25, Young inclines to the sup- 

 position that this difference proves that the solar atmosphere 

 really sweeps forward over the underlying surface. Careful 

 measurement of a line in the B group, which is due to at- 

 mospheric absorption, gave no displacement, as was to be 

 expected. 



Duboscq has contrived some simple and novel optical pro- 

 jection experiments. By means of a lens, the image of a 

 small round hole is thrown on a screen ; between the lens 

 and the screen an Amici direct-vision prism is placed, capa- 

 ble of rotation about its axis. On rotating, the spectrum is 

 circular red within, violet without. Using polarized light 

 and a double-image rotating prism, the extraordinary image 

 describes around the ordinary as a centre a luminous ring, 

 crossed by a black line parallel to the plane of polarization. 

 The experiment may be varied by interposing a plate of 

 quartz. 



E<-oroff has described a differential electro -actinometer 

 devised in order to determine the coefficients of absorption 

 of the ultra-violet rays by different bodies. For this pur- 



