ASTRONOMY WITH AN OPERA-GLASS. 491 



ion entertained by some selenographers, and apparently justified by 

 observation. The enormous changes of temperature, from burning 

 heat under a cloudless sun to the freezing cold of space at night with 

 no atmospheric blanket to retain heat (which has generally been as- 

 sumed to be the condition of things on the moon), would be expected 

 to exert a disintegrating effect upon the lunar rocks. But the question 

 is now in dispute whether the surface of the moon ever rises above the 

 freezing-point of water, even under a midday sun. 



The Sun. That spots upon the sun may be seen with no greater 

 optical aid than that of an opera-glass is perhaps well known to many 

 of my readers, for during the past half dozen years public attention 

 has been drawn to sun-spots in an especial manner, on account of their 

 supposed connection with meteorology, and in that time there have 

 been many spots upon the solar disk which could not only be seen with 

 an opera-glass, but even with the unassisted eye. At present we are 

 approaching a minimum period of sun-spots, and the number to be 

 seen even with a telescope is comparatively very small, yet only a few 

 days before this page was written there was a spot on the sun large 

 enough to be conspicuous with the aid of a field-glass. During the 

 time of a spot-maximum the sun is occasionally a wonderful object, no 

 matter how small the power of the instrument used in viewing it may 



Fig. 4. The Sun. September 1, 1863. 



be. Strings of spots of every variety of shape sometimes extend com- 

 pletely across the disk. Our fourth illustration shows the appearance 

 of the sun, as drawn by the author on the 1st of September, 1883. 

 Every one of the spots and spot-groups there represented could be seen 

 with a good field-glass, and nearly all of them with an opera-glass. 



