264 Chronicles of Science. [April, 



each of the components of y Virginis, is entirely factitious, and owing 

 simply to the brightness of its light. This may be verified by repeat- 

 ing the determination with any one of the planets Mars, Uranus, 

 Neptune, or with the satellites of Jupiter. It will be remarked that 

 the apparent diameters of these objects do not decrease by diminishing 

 the brightness when they subtend a sensible angle in the instrument 

 employed with the prismatic glass. 



The subject of solar physics has attracted a great deal of attention 

 lately, and an important memoir on the nature of solar spots has lately 

 been communicated to the Royal Society, by Warren De la Eue, 

 F.R.S., Balfour Stewart, F.R.S., and Benjamin Loewy, Esq. The 

 authors have attempted to answer the following questions : — 



1. Is the umbra of a spot nearer the sun's centre than the pen- 

 umbra ? or, in other words, is it at a lower level ? 



2. Is the photosphere of our luminary to be viewed as composed of 

 heavy, solid, or liquid matter, or is it of the nature of either gas or 

 cloud ? 



3. Is a spot (including both umbra and penumbra) a phenomenon 

 which takes place beneath the level of the sun's photosphere or 

 above it. 



In answering the first of these it was shown that if the umbra is 

 appreciably at a lower level than the penumbra, we are entitled to 

 look for an apparent encroachment of the umbra upon the penumbra on 

 that side which is nearest the visual centre of the disc. Tables are 

 given in the paper showing the relative disposition of the umbra and 

 penumbra for each spot of the Kew pictures available for this purpose. 

 From the first table it is shown that 86 per cent, of the cases are in 

 favour of the hypothesis that the umbra is nearer the centre than the 

 penumbra, whilst 14 per cent, are against it. From the second table, 

 in which only spots of high latitude are considered, 809 per cent, are 

 in favour of the hypothesis, whilst 19*1 per cent, are against it. The 

 result of these tables shows, therefore, that the first question may be 

 answered in the affirmative. 



When discussing the second and third questions, it was observed 

 that the great relative brightness of faculas near the limb leads to the 

 belief that these masses exist at a high elevation in the solar atmo- 

 sphere, thereby escaping a great part of the absorptive influence which 

 is particularly strong near the border ; and this conclusion was con- 

 firmed by certain stereoscopic pictures produced by Mr. De la Rue, 

 in which the faculse appear greatly elevated. It was remarked 

 that faculse often retain the same appearance for several days, as 

 if their matter were capable of remaining suspended for some time. 

 From an examination of tables showing on which side of the sun-spots 

 their accompanying faculae are mostly found, it would appear as if 

 the luminous matter, being thrown up into a region of greater abso- 

 lute velocity of rotation, fell behind to the left, and we have thus 

 reason to suppose that faculous matter which accompanies a spot is 

 abstracted from that very portion of the sun's surface which contains 

 the spot, and which has in this matter been robbed of its luminosity. 



Again, there are a good many cases in which a spot breaks up, in 



