The Nature of Experiment.

Hitherto I have gone no further than the region of experience and observa­tion, from which, Jevons says, “all knowledge proceeds.” There has been abundance of observa­tion of phenomena in this quest and I have ventured even on hypothesis. Experiment is shortly defined by Jevons as observa­tion plus altera­tion of conditions. He points out that when we make an experiment we more or less influence the events which we observe, as when we bring together certain substances under various conditions of temperature, pressure, electric disturbance or chemical action and so on, and then record the changes observed; and, that experiment may be of two kinds, experiments of simple fact and experiments of quantity. It is unnecessary here to describe all the rigorous rules that the man of science so rightly imposes upon himself before he claims to have proved his hypothesis, merely adding that among others he requires, Exclusion of Indifferent Circumstances, Simplifica­tion of Experiments, Removal of Usual Conditions, Removal of Interference of Unsuspected Conditions, Blind or Test Experiments, Negative Results of Experiment, and he lays down the limits of experiment. Those who have not for themselves investigated some scientific problem may learn from this statement some of the difficulties of the work of scientific men and will not fail to respect and admire the caution, patience and honesty of the scientific worker, and will perhaps feel the more gratitude to a class of men by whose self-denying labours they live and move and have their being in a modern state, and by whose discoveries, thus established, they are frequently preserved from premature death.