incidents. The accumulation of experimental data, pointing more or less exactly to physical relations of which no sufficiently precise theoretical account has yet been forthcoming, is doubtless largely responsible for the prevalent doctrine that theoretical development is of value only as an auxiliary to experiment, and cannot be trusted to effect anything constructive from its own resources except of the kind that can be tested by immediate experimental means. The mind will however not readily give up the attempt to apprehend the exact formal character of the latent connexions between different physical agencies: and the history of discovery may be held perhaps to supply the strongest reason for estimating effort towards clearness of thought as of not less importance in its own sphere than exploration of phenomena. Thus for example, the present view of the atomic character of electricity, which is at length coming within the scope of direct experiment, has been in evidence with gradually increasing precision ever since theoretical formulations were attempted on this subject: in fact if the considerations explained below (§ 46) are valid, it is the only view that could logically be entertained without involving either a reconstruction of the accepted basis of physical representation or else an admission of its partial or merely illustrative character.
Some of the following chapters may be regarded as a re-statement in improved form of investigations already developed in a series of memoirs, Phil. Trans. A 1894-6-7. They cover only a part of the survey that was there attempted, being concerned mainly with the systematic construction of general electric theory on the basis of intrinsic atomic charges. Judging from some criticisms which that method has attracted, it would appear that misconception has existed owing to difficulty in attaining the point of view, such as may possibly arise from the circumstance that the fundamental concept of the electron did not there present itself at the beginning of the discussion, but was introduced subsequently in an appendix. In estimating the value of an undertaking of this kind, it should of course be
