132 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



the properties of the huge mass — what, for example, will be its output 

 of heat and li^ht, what will be its period if it is sot pulsating. Cal- 

 culate "according to the laws of physics as known to terrestrial 

 experiment"; and then turn to the man with the telescope and ask, "Is 

 that anythmg like the stars you come across in the sky?" It may be 

 that he will point out differences. If the stars have anything new to 

 reveal to us — which the physicist with his limited conditions of experi- 

 ment has been unable to foresee — we shall in this way sort it out from 

 that which is a direct consequence of what we ah'eady know or think 

 we know. 



Investigations which follow this course of i)rocedure are clearly 

 not speculative. They may have other faults, and their conclusions 

 may be uncertain; but their method is the very opposite to flighty 

 conjecture. Parenthetically, may I ask whether it is not possible for 

 critics of theoretical investigations of the stars to find some other 

 term of disapprobation than the term "speculative" ; one prefers to have 

 even one's faults called by the right name. I do not class all specula- 

 tion as a fault; and it has sometimes happened that important ad- 

 vances have l)Ogun in a speculative way. The real harm is when 

 speculative attempts are not sufliciently discriminated from the 

 straightforward application of existing knowledge. And the con- 

 verse is no less harmful— when Lane's pattern of investigation, that is 

 to saj'^, the results of applying on the stellar scale the laws found in 

 the laboratory, is confused with the frankly speculative theories that 

 have at times been put forward ; and (perhai)s I may add for the bene- 

 fit of the mathematicians hero) worst of all, when stars constituted of 

 matter obeying the laws of physics so far as they have been unraveled 

 to-day, are confused with mathematical creations whose only claim 

 on our attention is that they satisfy elegant differential equations. 



I will not guarantee that the conclusions that I shall put before you 

 will survive the progress of loiowledge in the next 50 ^''ears. If by 

 then the stars of gaseous constitution which wo accept today have 

 given place to liquid stars or solid stars or, as I once suggested, crys- 

 talline stars composed of gaseous crystals — well, there have been more 

 surprising changes in science than that. But I believe firmly that the 

 conclusions are such as fit our present scientific Icnowledge; and that 

 they represent present-day astronomy in step with present-day 

 physics. To use a rather favorite word nowadays, unification, the 

 interest of these investigations is, I think, not so much dependent on 

 the absolute information they yield, as in the unification of physics 

 and astrophysics — enabling us to see one underlying cause or one 

 elementary equation at the root of the most diverse manifestations, 

 tracing its effects in the vacuum tube, in the interior of stars, in the 

 diffuse nebulae, and — not least — in the system of galaxies which con- 

 stitutes the cosmos. 



