"But waiving this refinement, it will be sufficient for our purpose to consider a single muscle as having a simple action, an action which cannot be sustained with uniformity a minute of time without actual pain, nor a second of time with positive pleasure. This, however, is not to be understood as an attempt to fix these limits with precision. To express the law in more general terms, as we diminish the duration of a muscle's action we diminish the pain until we arrive at an action whose attendant sensation is neutral, i. e., neither painful nor pleasurable; as soon as we have passed that point and have begun to execute motions a little more transient, the attendant sensation becomes positively pleasurable, and the pleasure increases as the separate actions become more transient. It is not necessary to infer that there is attending each action of shorter duration a pleasure exceeding that which attends each action of greater duration; for the more transient actions are, in a given time, more numerous; so that with the same amount of pleasure for each muscular contraction, the amount of pleasurable sensation in a given time--say a second--would exceed the amount attending the less frequent and more prolonged actions in the same period: a greater number of separate impressions become--so to speak--crowded together and condensed, and thus produce a more vivid pleasure. Several contiguous impressions thus conspire to heighten the contemporaneous effect, inasmuch as we are unable to distinguish those impressions which are made at very short intervals on the muscular sense, any more than we are those made at very short intervals on the retina. We have an example of the latter in the familiar experiment of swinging a coal of fire in a circle, and in various optical instruments for combining colors and images. "The proposition which I have endeavored to establish is, that there is a neutral point to which, if constant action is prolonged, its pleasurable character begins to be reversed; that the vividness of the sensation increases with the distance from this point, being on the one side pleasurable, on the other painful; the more transient the actions are, the more pleasurable; the more prolonged they are, the more painful. "I am of opinion that this physiological principle is susceptible of interesting applications to a class of pleasures, which metaphysicians have regarded as exclusively mental, and dependant upon certain supposed ultimate principles of the constitution of mind, principles not resolvable into others more elementary. As physiology shall advance, it may be expected that many of these imaginary elements will yield to its searching analysis. Whether the writer has been so fortunate as to resolve any of the generally admitted elements of mental taste, the reader will be able to judge from the sequel.