654 Chronicles of Science. [Oct., 



reflected from it is white, or greenish-white. The greenish tinge may 

 possibly arise from contrast with the ruddy centre. 



On the whole, the impression appears to be, that Mars has not 

 usually a very cloudy atmosphere. During the last opposition the 

 permanence and nearly equable distinctness of the principal features 

 under similar circumstances was surprising. On no occasion could 

 Mr. Dawes satisfactorily make out that any part was decidedly less 

 distinct than might be expected from the appearance of the other 

 features then visible. 



Another paper by Mr. Dawes was on an aperture-diminishing eye- 

 piece and a photometer of neutral tint glass. By the former arrange- 

 ment the aperture of the object glass can be virtually diminished to 

 any desirable extent without disturbing the telescope to vary the 

 aperture on the object glass. The great convenience of this arrange- 

 ment is too obvious to need further comment. 



The other jmotometric arrangement consists in the addition to the 

 solar eye-piece of one or more sliding wedges of neutral-tint glass ; 

 the obscuration extending from the smallest possible to what is usually 

 sufficient for the Sun. A capital advantage of this arrangement is, 

 that the small apertures in the diaphragm of the solar eye-piece 

 enable one of the components of a double star to be excluded from 

 the field while the brightness of the other is measured : — obviously a 

 very necessary precaution where the stars differ greatly in brightness. 

 As an example, it may be stated that the very small star near a, Lyrce 

 appears, when the large star is in the field with it, to be about of 

 mag. 11*2 of Struve's scale ; but, on excluding the large star, it rises 

 to about 9 '7, a difference of 1^ magnitude. In the same way the 

 comparative brightness of different portions of the Moon may be 

 determined by isolating them in a small field. Thus also the 

 brightness of the solar illumination of dur atmosphere may be com- 

 pared with that of the photosphere of the Sun itself, and also 

 different parts of the photosphere. 



Some good observations on the photosphere of the sun have been 

 communicated by Mr. Fletcher. He comes to the conclusion that the 

 appearance of the interlacing of long, flat, lenticular-shaped objects 

 is due to a tremulous atmosphere, for the moment the atmosphere 

 became steady the appearance vanished; and when vision was most 

 perfect the idea of interlacing could not be entertained. The result 

 of this examination of the sun's disc with an instrument of unexcelled 

 defining power and under atmospheric circumstances such as rarely 

 occur, is a strong impression that the granules are not " entities " at 

 all, but portions of the sun's luminous envelope raised high in the 

 outer and non-luminous atmosphere. 



Some very elaborate observations on the solar photosphere and 

 sun-spots follow by Mr. Brodie and Mr. Lockyer. Each of these 

 papers is illustrated with woodcuts. The former gentleman's observa- 

 tions appear to show that the rice-grains and willow-leaves must not 

 be confounded with each other, as (according to Mr. Nasmyth's 



