“Some time ago I worked with several colleagues in the laboratory of a High School on a series of complicated experiments in elasticity, a piece of work we had undertaken voluntarily; it was beginning to take up more time, however, than we had anticipated. One day, as I went into the laboratory with my friend F., he remarked how annoying it was to him to lose so much time to-day as he had so much to do at home; I could not help agreeing with him and said half-jokingly, referring to an occasion the week before: ‘Let us hope the machine will break down again so that we can stop work and go home early.’ In arranging the work it happened that F. was given the regulation of the valve of the press; that is to say, he was, by cautiously opening the valve, to let the liquid pressure out of the accumulator slowly into the cylinder of the hydraulic press. The man who was conducting the experiment stood by the pressure gauge, and, when the right pressure was reached, called out loudly, ‘Stop.’ At this command F. seized the valve and turned with all his might—to the left! (All valves without exception close to the right.) Thereby the whole pressure in the accumulator suddenly came into the press, a strain for which the connecting-pipes are not designed, so that one of them instantly burst—quite a harmless accident, but one which forced us, nevertheless, to cease work for the day and go home. It is characteristic, by the way, that not long after, when we were discussing the affair, my friend F. had no recollection whatever of my remark, which I recalled with certainty.” So with this in mind you may begin to suspect that it is not always a mere chance which makes the hands of your servants such dangerous enemies to your household effects. And you may also raise the question whether it is always an accident when one injures oneself or exposes oneself to danger—ideas which you may put to the test by analysis when you have an opportunity.