Spectrum Analysis 157 



applied for the first time the ideas of the principle of con- 

 servation of energy to the subject, by considering an enclosure 

 impermeable to heat radiations and at a uniform temperature. 

 This led him to the conclusion that the internal radiation 

 must everywhere be the same and only depend on temperature. 

 The rest follows easily : absorption and radiation must bear 

 a constant relation to each other in such an enclosure. He 

 illustrated the results by many striking experiments. 



Much has been written about the relative merits of 

 several observers who anticipated, in various directions, the 

 great work of Kirchhoff and Bunsen. But the history of 

 science should not aim at assigning marks of merit to 

 different investigators. What interests us is how a great 

 generalization gradually matures, how it begins frequently 

 with the observation of isolated facts, generally overlooked 

 at first because their importance is not recognized. It may 

 be that some link between the disconnected observations is 

 wanting; it may be that experiment has gone ahead of 

 theory or theory may be waiting to be confirmed by ex- 

 periment. When the time is ripe, someone with a better 

 appreciation of the significance of the facts or a deeper 

 insight into their mutual connexion touches the matter 

 with a master hand, and presents it in a form which carries 

 conviction. Though he may have worked in ignorance of 

 what has been done before, he has worked in an atmosphere 

 in which previous ideas and tendencies of thought have 

 been absorbed, and in general he owes something to the 

 pioneers who have gone before him. In some cases the 

 succession of events which lead to a discovery may be 

 compared to what would happen if a delicate balance carried 

 on one side the arguments in favour of a new idea, and 

 on the other hand the objections which are brought against 

 it. At first the side that bears the objections is much the 

 heaviest; as time goes on the difference becomes less 

 marked, sometimes by the removal of objections, but more 

 frequently by increased evidence in favour of the new idea. 

 Ultimately when sufficient weight is put on that side, a point 

 is reached when the balance tips over. This is the psycho- 

 logical moment when the discovery is accepted, and he 

 who adds the last grain is technically the discoverer. Those 



