456 THE POPULAR SCIENCE MONTHLY. 



any participant in the excellent work of that organization, he can not, 

 in good English, be less than an assistant, and yet only officers of the 

 highest attainable grade are entitled to the latter distinction. Still 

 below the assistants and sub-assistants come the aids, young officers 

 whose inferiority of position is mollified by the possession of a title 

 synonymous in meaning with that of their superiors, and therefore 

 equally respectable in the popular comprehension. Such is the pov- 

 erty of this nomenclature that it carries with it only the general idea 

 of subordination. Surely it would not be impossible to devise some 

 system of titles which would at the same time convey some hint of 

 the duties and the relative rank of the scientists of that body. 







ON KADIATION * 



By JOHN TYNDALL, F.E.S. 



SCIENTIFIC discoveries are not distributed uniformly in time. 

 They appear rather in periodic groups. Thus, in the first two 

 years of this century, amoug other gifts presented by men of science 

 to the world, we have the voltaic pile ; the principle of Interference, 

 which is the basis of the undulatory theory of light ; and the discov- 

 ery by William Herschel of the dark rays of the sun. 



Directly or indirectly, this latter discovery heralded a period of 

 active research on the subject of radiation. Leslie's celebrated work, 

 " On the Nature of Heat," was published in 1804, but he informs us, 

 in the preface, that the leading facts which gave rise to the publica- 

 tion presented themselves in the spring of 1801. An interesting but 

 not uncommon psychological experience is glanced at in this preface. 

 The inconvenience of what we call ecstasy, or exaltation, is that it is 

 usually attended by undesirable compensations. Its action resembles 

 that of a tidal river, sometimes advancing and filling the shores of 

 life, but afterward retreating and leaving unlovely banks behind. 

 Leslie, when he began his work, describes himself as " transported at 

 the prospect of a new world emerging to view." But further on the 

 note changes, and before the preface ends he warns the reader that he 

 may expect variety of tone, and perhaps defect of unity, in his disqui- 

 sition. The execution of the work, he says, proceeded with extreme 

 tardiness ; and, as the charm of novelty w r ore off, he began to look 

 upon his production with a coolness not usual in authors. 



The ebb of the tide, however, was but transient ; and to Leslie's 



ardor, industry, and experimental skill, we are indebted for a large 



body of knowledge in regard to the phenomena of radiation. In the 



prosecution of his researches he had to rely upon himself. He devised 



* A " Friday Evening Discourse," recently delivered in the Royal Institution. 



