If, then, by the original question, how many objects can we attend to at once, be meant how many entirely disconnected systems or processes can go on simultaneously, the answer is, _not easily more than one, unless the processes are very habitual; but then two, or even three_, without very much oscillation of the attention. Where, however, the processes are less automatic, as in the story of Julius Cæsar dictating four letters whilst he writes a fifth, there must be a rapid oscillation of the mind from one to the next, and no consequent gain of time. * * * * * When the things to be attended to are minute sensations, and when the effort is to be exact in noting them, it is found that attention to one interferes a good deal with the perception of the other. A good deal of fine work has been done in this field by Professor Wundt. He tried to note the exact position on a dial of a rapidly revolving hand, at the moment when a bell struck. Here were two disparate sensations, one of vision, the other of sound, to be noted together. But it was found that in a long and patient research, the eye-impression could seldom or never be noted at the exact moment when the bell actually struck. An earlier or a later point were all that could be seen. =The Varieties of Attention.=--Attention may be divided into kinds in various ways. It is either to _a_) Objects of sense (sensorial attention); or to _b_) Ideal or represented objects (intellectual attention). It is either _c_) Immediate; or _d_) Derived: immediate, when the topic or stimulus is interesting in itself, without relation to anything else; derived, when it owes its interest to association with some other immediately interesting thing. What I call derived attention has been named 'apperceptive' attention. Furthermore, Attention may be either _e_) Passive, reflex, involuntary, effortless; or _f_) Active and voluntary. _Voluntary attention is always derived_; we never make an _effort_ to attend to an object except for the sake of some _remote_ interest which the effort will serve. But both sensorial and intellectual attention may be either passive or voluntary. In _involuntary attention_ of the _immediate sensorial_ sort the stimulus is either a sense-impression, very intense, voluminous, or sudden; or it is an _instinctive_ stimulus, a perception which, by reason of its nature rather than its mere force, appeals to some one of our congenital impulses and has a directly exciting quality. In the chapter on Instinct we shall see how these stimuli differ from one animal to another, and what most of them are in man: strange things, moving things, wild animals, bright things, pretty things, metallic things, words, blows, blood, etc., etc., etc.