180 ANNUAL OF fcCIEXTIFIC DISCOVERY. 



casionally useful towards the limb of the sun. He described the 

 bright streaks or facula? as of diversified form and distinct outline, 

 either entirely separate or coalescing in various ways into ridges and 

 network. When the spots became invisible near the limb, the un- 

 dulated shining ridges and folds still indicated their place, being more 

 remarkable thereabout than elsewhere on the limb, though almost 

 everywhere traceable in good observing weather. In a diagram 

 made on the 29th of March last, faculae are shown in the most brilliant 

 parts of the sun. They appear of all magnitudes, from barely dis- 

 cernible, softly-gleaming spots a thousand miles long, to continuous, 

 complicated, and heaped ridges 40,000 and more miles in length, and 

 1,000 to 4, 000 miles and more broad. They are never regularly 

 arched, and never found in straight bands, but always devious and 

 minutely undulated, like clouds in the evening sky or very distant 

 ranges of snowy mountains. When minutely studied, the ridges ap- 

 pear prominent in cusps and depressed into hollows. By the frequent 

 meeting of the bright ridges, spaces of the sun's surface are included 

 of various magnitudes, and forms somewhat corresponding tc the 

 areas and forms of the irregular spots with penumbras. Kidges of 

 this kind often embrace and inclose a spot, though not very closely, 

 the spot appearing more conspicuous from the surrounding brightness ; 

 but sometimes there appears a broad white platform round the spot, 

 and from this the white crumpled ridges pass in various directions. 

 Towards the limb the ridges appear nearly parallel to it : further off this 

 character is exchanged for indeterminate direction and lessened dis- 

 tinctness ; over the rest of the surface they are less conspicuous, but can 

 be traced as an irregular network, more or less designated by that struc- 

 ture which has been designated as porosity. The faculaa preserve their 

 shapes and position, with no visible change during a few hours of obser- 

 vation, and probably for much longer periods. They do not appear to 

 project beyond the general circular outline of the sun, a circumstance 

 which the author explains without denying that they actually do rise 

 above the general surface, whether as clouds or mountains, to either 

 of which they may be truly likened. In respect to porosity, the 

 author had also devoted much time to a scrutiny of the interspaces 

 between the faculae towards the limb and the general surface 

 towards the interior of the disc. Towards the interior the ground 

 acquires more evident lights and shades, a sort of granulation difficult 

 to analyze. Under favorable conditions for observation, there ap- 

 pears little or none of that tremor and internal motion described by 

 earlier observers. What is then seen is a complicated surface of in- 

 terrupted lights and the limits of which appear arched or straight or 

 confused, according to the case; and the indeterminate union of 

 these produces sometimes faint luminous ridges, the intervals filled 

 up by shaded interstices and insulated patches of illuminated surface. 

 The best resemblance to these complicated small surfaces of light and 

 shade he had been able to procure was a disc of a particular sort of 

 white paper placed near the eye-end of the telescope, and seen by 

 transmitted light. Heaps of small fragments of white substances, not 

 so uniform in figure or equal in size as rice grains, might also be 

 suggested for comparison. 



Origin of Solar Spots. Sir John Herschel, in an article in The Quar- 



