no 



Progress in Physils. 



[January, 



placed parallel to the hour-circle. This indicates a length of at least 130,000 

 miles, without allowing anything for the foreshortening resulting from the 

 nearness of the sun's limb. By 5 o'clock the clouds had nearly disappeared ; 

 a little rack alone remained. In the telescope this group of spots, from their 

 first appearance, exhibited a strong yellowish tinge, which appeared to overlie 

 all the central portion of the cluster. So conspicuous was it that several 

 persons, unaccustomed to astronomical observation, noticed it at once before 

 their attention was called to it. The penumbra of the group was unusually 

 faint. 



At a late meeting of the Manchester Photographic Society, Mr. Kershaw 

 showed some very interesting photographs, illustrating one of the many uses 

 made of photography in the war raging on the Continent. The subject con- 

 sisted of the important portions of Paris newspapers cut out, arranged in 

 columns, and photographed on talc. What would form nine columns of a 

 newspaper was copied on a space about two inches by one inch and a half, 

 and was perfectly legible with a glass of moderate magnifying power. These 

 talc photographs left Paris by balloon post. 



Mr. Browning, the eminent optician, has arranged a spectroscope in which 

 the prisms are automatically adjusted for the minimum angle of deviation for 

 the particular ray under examination. In spectroscopes of ordinary construc- 

 tion, when several prisms are employed, a great deficiency of light will" be 



Fig. 19. 



noticed towards the more refrangible end of the spectrum. This arises from 

 the fact that the prisms are adjusted to the minimum angle of deviation for 

 the most luminous rays which occupy the middle of the spectrum. Fig. 19 

 shows the method in which the change in the adjustment of the prisms to the 

 minimum angle of deviation for each particular ray is made automatically. In 

 this diagram, p p, &c, represent prisms; all of which prisms, with the 

 exception of the first, are unattached to the plate on which they stand, the 

 triangular stand on which the prisms are hinged together at the angles 



