Is it not clear, therefore, that to observe correctly is by no means easy? On the one hand, a pre-conception, makes {167} us liable to see things not quite as they are, but as we think them. On the other hand, in the absence of a pre-conception, we are liable to pass over much that we ought to see. Yet we must have either a pre-conception or no pre-conception. Evidently, then, all our observations, save those guided by true theories already reached, are in danger of either distortion or incompleteness. It remains but to remark, that if our observations are imperfect in cases like the foregoing, where the things seen are persistent, and may be again and again looked at or continuously contemplated; how much more imperfect must they be where the things seen are complex processes, changes, or actions, each presenting successive phases, which, if not truly observed at the moments they severally occur, can never be truly observed at all! Here the chances of error become immensely multiplied. And when, in addition, there exists some moral excitement,—when, as in these Spirit-rapping and Table-turning experiments, the intellect is partially paralysed by fear or wonder correct observation becomes next to an impossibility. {168} WHAT IS ELECTRICITY? [_First published in_ The Reader _for November 19, 1864._] Probably few, if any, competent physicists have, of late years, used the term “electric fluid” in any other than a conventional sense. When distinguishing electricity into the two kinds, “positive” and “negative,” or “vitreous” and “resinous,” they have used the ideas suggested by these names merely as convenient symbols, and not as representatives of different entities. And, now that heat and light are proved to be modes of motion, it has become obvious that all the allied manifestations of force must be modes of motion. What is the particular mode of motion which constitutes electricity, thus becomes the question. That it is some kind of molecular vibration, different from the molecular vibrations which luminous bodies give off, is, I presume, taken for granted by all who bring to the consideration of the matter a knowledge of recent discoveries. Beyond those simple oscillations of molecules from which light and heat result, may we not suspect that there will, in some cases, arise compound oscillations? Let us consider whether the conditions under which electricity arises are not such as to generate compound oscillations; and whether the phenomena of electricity are not such as must result from compound oscillations.