152 Intelligence and Misce/laneons Articles. 



a distance by means of a little telescope of small magnifying power, 

 provided with a diaphragm corresponding in extent to the ])upil of 

 the human eye. Under these conditions the apparent image is 

 formed in its different parts by the different elements of the mirror ; 

 and if these elements have not a common focus, an image of the 

 distortions results, which, suitably interi)reted, lead to the discovery 

 of the faults of the rays of curvature corresponding to the different 

 parts of the mirror. 



The third process shows directly, by a comprehensive view, the 

 alterations of form reflected on the figure which the mirror ought 

 to present under the circumstances in which the trial is made. The 

 mirror is so arranged as to give in space the image of a narrow 

 orifice pierced in an opake plate, and vividly illuminated by artificial 

 light. This image is almost totally masked by an opake screen with 

 rectangular edge. The rays, which in passing graze the edge, are 

 received directly on the eye, and give an image of the surface of the 

 mirror which is perceived in light and shade, and in which all the 

 reflexions capable of altering the exact convergence of the entire 

 pencil are presented in exaggerated relief. From this the parts are 

 discovered where the corrections ought to be brought, which is ac- 

 cordingly done. 



The same methods of examination may also be applied to the 

 achromatic objectives of telescopes, and allow the application of the 

 same system of local corrections. — Comptes RendiLf, Dec. 20, 1858. 



ON SOME LARGE SOLAR SPOTS. BY W. R. DAWES. 



Sir, — There is now visible an enormous mass of spots on the 

 sun's disc, composed of two distinct groups near together, each of 

 which has a large spot with many smaller ones near it. Without 

 telescopic aid a sharp eye, properly defended with a dark glass of 

 good colour, will readily see them as two small black spots, very close 

 together, a little below the centre and to the right hand of it. With 

 a powerful telescope they are wonderful and instructive. The east- 

 ern large spot is especially so, as exhibiting very distinctly the dark, 

 mottled, cloudy stratum, with the black opening, constituting the 

 true nucleus, nearly in the middle of it. 



It is much to be regretted that the photographic art has not yet 

 succeeded in exhibiting any of the details of these interesting phae- 

 nomena ; and to depict them correctly with the pencil is most labo- 

 rious, if not absolutely impossible. Moreover, the changes in the 

 minuter details are often so great and so rapid, that, if perfectly cor- 

 rect pictures could be obtained from day to day, they would agree 

 only in their general features. The successful application of pho- 

 tography to this department of astronomical observation is surely 

 worthy of all the ingenuity which could be brought to bear upon it. 

 —Times, Jan. 28, 1859. 



