May 13, 1898.] 



SCIENCE. 



659 



worthy considering the fact that such an 

 ■ohject as the great cluster in Hercules con- 

 tains not more than two or three variable 

 stajfs, while the Harvard plates show that 

 the cluster Messier 3 contains 132 variables. 

 This is only one instance out of many of 

 the striking efficiency of the photographic 

 work which is being carried on under Pro- 

 fessor Pickering's able direction. 



It may be well to introduce here a few 

 words regarding the magnifying powers em- 

 ployed in actual observations. The opti- 

 mistic writer, who is planning to photo- 

 graph houses on Mars, believes that his 

 recent invention will render possible the 

 use of powers as high as a million diam- 

 eters, and even greater, so that if men 

 exist upon the planets they can easily be 

 seen. Astronomers know nothing of such 

 powers in practice. For double-star obser- 

 vations, with the largest telescope and under 

 "the most perfect conditions, powers as high 

 as 3,700 diameters have occasionally been 

 •used. But in regular work it is not a com- 

 mon thing to exceed 2,700 diameters. Under 

 Tery exceptional circumstances the Moon 

 might perhaps be well seen when magnified 

 2,000 diameters, but this would be an ex- 

 treme case, and in general a much better 

 view could be had with powers ranging 

 from 500 to 1,000. Jupiter can rarely be 

 well seen with a power greater than four or 

 five hundred, though Saturn will stand con- 

 siderably higher magnification. Mars is 

 best seen with a power of five or six hun- 

 dred. With small telescopes lower powers 

 are generally used. The difficulty is not in 

 finding optical means to increase the mag- 

 nification, as some of these newspaper 

 writers seem to imagine. It is rather a 

 question of being able to see anything but 

 a confused luminous object after the high 

 eyepieces have been applied. The more or 

 less disturbed condition of the Earth's 

 atmosphere is mainly responsible for this, 

 -but it is doubtful whether, with even per- 



fect conditions, such an object as Jupiter 

 could be advantageously submitted to great 

 magnification. 



During the present century there has 

 grown up side by side with astronomy, to 

 which it in fact owes its existence, the new 

 science of astrophysics. In a broad sense 

 this science may properly be classed as a 

 department of astronomy, but at the present 

 time its interests are so manifold, its meth- 

 ods so distinct, and its relationship to pure 

 physics so pronounced, that it may fairly 

 claim to be considered by itself as a coor- 

 dinate branch of science. While astronomy 

 deals more especially with the positions 

 and motions of the heavenly bodies, it is 

 the province of astrophysics to inquire into 

 their nature and to search out the causes 

 for the peculiar celestial phenomena which 

 the special instruments at the disposal of 

 the astrophysicist bring to light. It should 

 be added that no hard and fast line can be 

 drawn between astronomy and astrophysics, 

 as one of the principal problems of the 

 latter subject involves just such determina- 

 tions of motion as are particularly to be de- 

 sired for the purposes of the astronomy of 

 position. The subjects are thus intimately 

 related and closely bound together, and the 

 bond between astrophysics and physics is 

 hardly less strong. They should thus be 

 cultivated together, so that they may mu- 

 tually assist one another in bringing about 

 the solution of the varied problems with 

 which they are concerned. 



It is particularly in astrophj'sical research 

 that a great telescope is advantageous. For 

 the principal instrument of the astrophysi- 

 cist, the spectroscope, it is necessary to 

 have as much light as can be gathered into 

 a single point. With sufficient light the 

 chemical analysis of the most distant star 

 resolves itself into a comparatively simple 

 problem. But with small telescopes and 

 consequently faint star images such anal- 

 ysis, except of a roughly approximate 



