PEOGUESS IN ASTRONOMY. 141 



wax and wane. Tacchina and Ricco, during the last thirty years, have 

 proved that the prominences follow suit, and the fact that the corona 

 also obeys the same law was established during the American eclipse 

 of 1878. ' 



The study of solar ph3"sics consists in watching and recording the 

 thermal, chemical, and other changes which accompany this period. 

 Some of these effects can be best studied during those times when the 

 ball itself is covered by the moon in an eclipse. Then the outer por- 

 tions of the sun are revealed in all their beauty and majesty, and all 

 the world goes to see. 



But it is the quiet daih" work in the laboratory which has enabled 

 us to study the sun's place in relation to the other stars, and so to 

 found a chemical classitication of all the stars that shine. 



From the sun we may pass to his svstem, and first consider the 

 nearest bod}" to us — the moon. 



While some astronomers have been discussing the movements and 

 evolution of our satellite, others have been engaged upon maps of its 

 surface, upon questions dealing with a lunar atmosphere, or a study 

 of the origin of the present conformations and of possible changes. 

 The science of selenology may be said to have been founded by 

 Schroter at the beginning of the century, but it required the applica- 

 tion of photography in later j^ears to put it on a firm basis. Maps of 

 the moon have been prepared by Lohrmann, Beer and Madler, and 

 Schmidt, the latter showing the positions of more than 30,000 craters. 



Ver}^ erroneous notions are held by some as to what we may hope to 

 do in the examination of the moon's surface b}' a powerful telescope. 

 A power of a thousand enables us to see it as if we were looking at York 

 from London. It is recorded that Lassell once said that with his largest 

 reflector in a "fit" of the finest definition he thought he might be able 

 to detect whether a carpet as large as Lincoln's Inn Fields was round 

 or square. LTnder these circumstances, then, we may well understand 

 that the question of changes on the surface has been raised from time 

 to time never to be absolutely settled one way or the other. By many 

 the existence of an atmosphere is denied, and this is a condition which 

 would negative changes, anything like the geological changes brought 

 about on the surface of the earth, l)ut the idea is now held by many 

 that there is still an atmosphere, though of great tenuity. 



The last few years of the century have been rendered memorable 

 from the lunar point of view by the publication and minute study of a 

 most admirable series of photographs of the moon obtained by the great 

 equatorial Coude of the Paris Observatory by Loewy and Puiseaux. 

 One of the chief points aimed at has been to determine the sequence of 

 the various events represented by the rilles, craters, and walled plains, 

 the mountain ranges and seas. This work is still in progress, the 

 fourth part of the atlas being published in 1900; bub enough has 



