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SCIENCE 



[N. S. Vol. XXXIV. No. 872 



us to a conclusion when they are marshaled by 

 the light of some leading idea. A theory is then 

 a necessity for the advance of science, and we may 

 regard it as the branch of a living tree, of which 

 facts are the nourishment. 



Those who have read the letters of 

 Charles Darwin will recognize that this 

 opinion was also held by the father, and 

 may have been adopted by the son. It is 

 no part of my purpose to raise any question 

 of originality: I mention the point merely 

 to take the opportunity it gives me of show- 

 ing that I do not approach lightly an opin- 

 ion held by two such men. With the ut- 

 most respect I wish to question whether the 

 criterion indicated goes deep enough. 

 Often have we had ocular demonstration 

 of the value of a theory in stimulating the 

 advance of science, but is advance wholly 

 dependent on the existence of a theory ? I 

 have tried to indicate already a deeper mo- 

 tive power by such instances as the work of 

 Tycho, who had no theory, but who per- 

 ceived the need of observation. And I will 

 now definitely formulate the view that the 

 perception of the need for observations, the 

 faith that something will come of them, and 

 the skill and energy to act on that faith — 

 that these qualities, all of which are pos- 

 sessed by any observer worthy the name, 

 have at least as much to do with the ad- 

 vance of science as the formulation of a 

 theory, even of a correct theory. The work 

 of the observer is often forgotten — it lies at 

 the root of the plant ; it is easier to notice 

 the theories which blossom and ultimately 

 produce the fruit. But without the patient 

 work of the observer underground there 

 would be neither blossom nor fruit. It is 

 also easy to fix attention on the mechanical 

 nature of much observation ; but this is not 

 the principal feature of observing any 

 more than is numerical computation of 

 mathematics. There are men like Adams 

 who perform gigantic numerical computa- 



tions faultlessly, but there are others who 

 would take equal rank as mathematicians 

 who can not do three additions correctly; 

 and again others who could compute well 

 and quickly but prefer to hand over that 

 part of their work to some one else. Simi- 

 larly some great observers themselves look 

 through the telescope, and some merely di- 

 rect others how to do so; the spark of di- 

 vine fire is not dependent on this detail, 

 but on the possession of the qualities above 

 mentioned — perception, faith, skill and 

 energy. 



By way of bringing out more fully the 

 nature of the assertion made by Sir George 

 Darwin, let me beg your attention to a 

 striking incident in recent astronomical 

 history. We all know how the great as- 

 tronomer we lost last year, Sir William 

 Huggins (one of those already mentioned 

 as having occupied the presidential chair 

 of the association without having filled that 

 of Section A), initiated the determination 

 of velocities of the heavenly bodies in the 

 line of sight by means of the spectroscope. 

 We know further how the accuracy of these 

 determinations was improved by the appli- 

 cation of photography, so that it has re- 

 cently become possible to measure the ve- 

 locity of the earth in its orbit (as it 

 alternately approaches and recedes from a 

 given star) with a precision which matches 

 that of other known methods. Now Mr. W. 

 W. Campbell, on his appointment as direct- 

 or of the Lick Observatory in 1900, per- 

 ceived the desirability of observing the line 

 of sight velocities of as many stars as pos- 

 sible, believed that that outcome would be 

 in some way for the advancement of sci- 

 ence, and resolutely acted on that belief, so 

 that for many years the resources of his 

 great establishment have been devoted to 

 this work. He has not turned aside from it 

 even to publish provisional results, and has 

 thereby incurred some adverse criticism. 



