364 ASTRONOMY 



coordinate diverse facts under a general formula, rule, or conception, 

 by means of which we can apprehend all the facts as parts of a single 

 entity. The value of this process of coordination is realized in two 

 ways. First, it is the means of referring otherwise disconnected 

 phenomena to a common origin. This is accomplished by means of 

 a formula which serves to connect them as parts of a greater whole. 

 Such a formula can then be grasped and brought into one field of 

 mental view. Secondly, this coordination may identify some fact, 

 or principle, in nature that not only serves to connect a group of 

 observed phenomena but itself also represents a real fact in nature. 

 The history of astronomy demonstrates that the investigator is not 

 deterred from an effort to gain possession of the element of value 

 first mentioned by any failure to grasp the second element. This is 

 not because the discovery of truths in nature, that have a real exist- 

 ence, is not regarded as the most valuable reward of research, but 

 because experience has shown that the invention of a satisfactory 

 formulation of observed phenomena ultimately leads to the discovery 

 of things which may be regarded as objectively real. In this sense 

 we may say that every successful representation of observed facts 

 through the adoption of a formulated conception results in scientific 

 truth. Examination of the manner in which astronomical research 

 has dealt with celestial motion will illustrate this idea. 



Until recent years the investigation of apparent celestial motion 

 has been by far the most important occupation of the astronomer. 

 Bessel defined it as essentially constituting the science of astronomy. 



We see the celestial motions as they are projected on the apparent 

 surface of the celestial sphere. We cannot vary our point of view at 

 will in order to see these motions in space qf three dimensions. From 

 our immediate perceptions we are wholly unable to form any reliable 

 opinion as to what they are really like, or as to the relative distances 

 separating the earth from celestial objects. The distances must be 

 derived from induction along with the other circumstances defining 

 the motions. Furthermore, the observer himself is in motion. His 

 motion is complicated. Enumerating only the most important, we 

 have, first, the motion of diurnal rotation; secondly, the annual 

 revolution of the earth around the sun as a centre; thirdly, a rapid 

 translatory motion through space of the earth along with the sun. 

 All these motions produce apparent motions of the celestial bodies 

 on the face of the sky; and these motions must be disentangled from 

 those which properly belong to those bodies. The first investigators 

 were in a specially unfavorable situation for successful research. 

 They were not even aware of the motions of the earth and sun. All 

 experience supported the impression of stability for the earth. It 

 was actually necessary to overthrow the direct testimony of the senses 

 before the system of celestial motions could be conceived as it actu- 



