“Don’t never prophsey onles ye know,” says Hosea Bigelow. I beg to call attention to the fact that this means “Don’t prophesy at all”--perhaps it was so meant by the shrewd Hosea. We never can know--and yet we continue to prophesy. The best we can do, of course, is to estimate probabilities. Probabilities! That is a good word. They have dropped it from the weather reports and call their estimate a “forecast.” I like the old word better. Let us see, then, what some of the probabilities are in library work. “Everything flows,” said the Greek philosopher. Nothing in the world is stable; change is the order of the day. But note the word he uses. That which flows is in a state of orderly change in a definite direction. Everything progresses; and the library and its work are being borne along in the general current. Now the writers on hydro-dynamics, who are experts on blow, tell us that there are two ways of studying a current, which they name the “historical” and the “statistical”: In the former the attention is fixed on a definite particle of the moving fluid whose change of velocity and direction is noted as it passes along; in the latter a definite locality of the stream is selected and the fluid’s changes of form and density at that particular place are observed. In like manner we may study the library movement historically or we can select a definite point in its course--the present time--and note the conditions and their alteration. The latter plan, I venture to think, is the more favorable one for the would-be prophet. Let us, then, take a few of the salient features of library work as they exist to-day and inquire: (1) What is the present situation with regard to each; (2) Is that situation changing; and whither and how fast; (3) Is its rate of change altering, and (4) are the conditions that affect it and its alteration, likely to remain as they are. If we can answer all these questions we can at least make an attempt at estimating the probable situation at a given future time. We must bear in mind, however, that in the library world, as elsewhere, there are sudden or abrupt changes, or catastrophes, and that these generally defy prediction. And this is equally true of unexpected aids or beneficient influences. The library benefactions of Mr. Carnegie would have upset the most careful and logical estimate of library progress made twenty years ago.