516 WRITINGS OF JOSEPH HENRY. [1877 



varying exhibitions which are presented to them. The sun 

 rises and sets, the seasons change, the heavens every night 

 present new aspects, but these to them are matters of course; 

 they excite no interest, and it is only when some extra- 

 ordinary phenomenon occurs, such as the blazing comet or 

 the startling earthquake, that their attention is arrested. 

 Another requisite is the power of the perception of truth, 

 which enables the observer to recognize and define with un- 

 erring accuracy what he has seen without any tinge of color 

 from a priori conceptions. Still another is the faculty of 

 eliminating accidental conditions from those which are essen- 

 tial ; and further, the characteristic of perseverance is indis- 

 pensable. 



The fields of scientific labor may be divided into two 

 classes, viz., those which relate to the empirical observation 

 of facts and those which relate to the systematic series of 

 investigations as to the law or cause of special phenomena. 

 As illustrations of the first class, may be specified the facts of 

 the phenomena of the physics of the globe, those of ordinary 

 meteorology and natural history ; while as examples of the 

 second, we have the phenomena of chemistry, physics, and 

 astronomy. 



The remarks I have previously made refer principally to 

 the former. In order to elucidate the method of investiga- 

 tion, in the latter case, I will suppose the existence of a new 

 phenomenon which is unconnected with an}^ of the present 

 generalizations of science, but of which it is desired to dis- 

 cover the law, or the facts with which it is associated. Such 

 facts standing alone form no part of science; they are 

 usually discovered in the course of investigations, and are 

 of great importance in pointing out fields of new research 

 which promise an abundant harvest. 



The first step in the investigation is to re-produce the 

 phenomenon ; the next is to form in the mind a provisional 

 hypothesis as to its cause ; and in the choice of this we are 

 governed by analogy. For example, if it appears to resem- 

 ble some of the phenomena of electricity, we assume that it 

 is produced by electricity ; we next endeavor to ascertain by 



