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152 of these various weights upon a certain volume of water with the results actually obtained by observation. Observations formed by variation of conditions on the basis of some idea or theory constitute experiment. Experiment is the chief resource in scientific reasoning because it facilitates the picking out of significant elements in a gross, vague whole.

Experimental thinking, or scientific reasoning, is thus a conjoint process of analysis and synthesis, or, in less technical language, of discrimination and assimilation or identification. The gross fact of water rising when the suction valve is worked is resolved or discriminated into a number of independent variables, some of which had never before been observed or even thought of in connection with the fact. One of these facts, the weight of the atmosphere, is then selectively seized upon as the key to the entire phenomenon. This disentangling constitutes analysis. But atmosphere and its pressure or weight is a fact not confined to this single instance. It is a fact familiar or at least discoverable as operative in a great number of other events. In fixing upon this imperceptible and minute fact as the essence or key to the elevation of water by the pump, the pump-fact has thus been assimilated to a whole group of ordinary facts from which it was previously isolated. This assimilation constitutes synthesis. Moreover, the fact of atmospheric pressure is itself a case of one of the commonest of all facts—weight or gravitational force. Conclusions that apply to the common fact of weight are thus transferable to the consideration and interpretation of the relatively rare and exceptional case of the suction of water. The suction pump is seen to be a case of the same kind or sort as the siphon, the