What more simple method than this could be desired?  Here we have the formation of the most valuable of all fuel gases at the cost of the coke and steam used, a gas also which has double the carrying power for hydrocarbon vapors possessed by coal gas, while its combustion gives rise to nothing but water vapor.

In this course of lectures I have left much unsaid and undone which I should have liked to have had time to accomplish, and if I have been obliged to leave out of consideration many important points, it is the time at my disposal and not my will which is to blame.  And now, in conclusion, I wish to express my thanks to my assistants, Messrs. J.A.  Foster and J.B.  Warden, who have heartily co-operated with me in much of the work embodied in these lectures.

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STEREOSCOPIC PROJECTIONS.

The celebrated philosopher Bacon, the founder of the experimental method, claimed that we see better with one eye than with two, because the attention is more concentrated and becomes profounder.  “On looking in a mirror,” says he, “we may observe that, if we shut one eye, the pupil of the other dilates.”  To this question:  “But why, then, have we two eyes?” he responds:  “In order that one may remain if the other gets injured.”  Despite the reasoning of the learned philosopher, we may be permitted to believe that the reason that we have two eyes is for seeing better and especially for perceiving the effects of perspective and the relief of objects.  We have no intention of setting forth here the theory of binocular vision; one simple experiment will permit any one to see that the real place of an object is poorly estimated with one eye.  Seated before a desk, pen in hand, suddenly close one eye, and, at the same time, stretch out the arm in order to dip the pen in the inkstand; you will fail nine times out of ten.  It is not in one day that the effects of binocular vision have been established, for the ancients made many observations on the subject.  It was in 1593 that the celebrated Italian physicist Porta was the first to give an accurate figure of two images seen by each eye separately, but he desired no apparatus that permitted of reconstituting the relief on looking at them.  Those savants who, after him, occupied themselves with the question, treated it no further than from a theoretical point of view.  It was not till 1838 that the English physicist Wheatstone constructed the first stereoscopic apparatus permitting of seeing the relief on examining simultaneously with each of the eyes two different images of an object, one having the perspective that the right eye perceives, and the other that the left eye perceives.