Solar Physics. 453 



analyzing many hundred observations, and show that the majo- 

 rity favour Wilson's supposition that the spot is a cavity with 

 the umbra for its lowest part. Their second question is — " is 

 the photosphere of our luminary to be viewed as composed of 

 heavy liquid or solid matter, or is it of the nature of a cloud ?" 

 An investigation into the known appearances presented by 

 faculas lead them to believe that they, and indeed the whole 

 photosphere of our luminary, are of the nature of a cloud, 

 and they suggest the following statement : " Solar faculse con- 

 sist of solid or liquid bodies of a greater or less magnitude, 

 either slowly sinking, or suspended in sequilibrio in a gaseous 

 medium." The writers give elaborate tables digesting- the 

 Kew observations on the relative position of faculse and spots, 

 and they say that out of 1137 cases, 584 have their faculse 

 either entirely or mostly on the left, while 508 have it nearly 

 equal on both sides, and only 45 mostly on the right." From 

 this they conclude that the faculse have been uplifted from the 

 very area occupied by a spot, and have fallen behind to the 

 left, from being thrown up into a region of greater velocity 

 of rotation. They likewise give reasons for supposing that 

 " a spot including both umbra and penumbra is a pheno» 

 menon which takes place beneath the level of the sun's 

 photosphere." 



Another important question relates to the probable com- 

 parative temperature of the darkest or lowest part of a spot. 

 The writers accept its lower luminosity as an indication of less 

 heat, and they conceive that a downward rush of a cold atmo- 

 sphere surrounding the photosphere gives rise to the appear- 

 ances that are observed. They say, " in conclusion we would 

 venture to suggest that if the photosphere of the sun be the 

 plane of condensation of gaseous matter, this plane may be 

 found to be subject to periodical elevations and depressions in 

 the solar atmosphere. It may be that at the epoch of mini- 

 mum spot-frequency this plane is uplifted very high in the 

 solar atmosphere, so that there is very little cold absorbing 

 atmosphere above it, and therefore great difficulty in forming 

 a spot. If this were the case, we might expect a less 

 atmospheric effect, or gradation of luminosity from the centre 

 to the circumference at the epoch of minimum than at that of 

 maximum spot-frequency. Perhaps on some future occasion 

 we may be able to produce evidence of this, and even of the 

 unequal atmospheric effect of the two limbs of the sun at the 

 same time; but in the mean time we shall content ourselves 

 with suggesting this to the observers of our luminary as a 

 simple inquiry that may possibly prove productive.'" 



The scientific world is deeply indebted to Messrs. De La 

 Hue, Stewart, and Loewy for many valuable remarks which the 



