Judging by means of the experience already acquired, we cannot reasonably expect that {22} discoveries fraught with such momentous consequences as those of magnetism or of galvanism and electro-magnetism, will be made very often. The progress of scientific discovery is gradual; we have at present but mere glimpses of the new world of truth which is being revealed to us by means of research; we are only at the very commencement of a knowledge of the inherent properties of matter and its forces, and consequently the methods we employ to utilize them are extremely imperfect. Matter has a general property of subdividing and transmuting forces; if we apply one force to a substance or machine, it produces many effects, not only those we want, but those also we do not want; when we heat a piece of iron, the heat produces a number of changes, mechanical, electric, magnetic, and chemical, and it is partly by means of what is termed the "internal resistance" of bodies that these effects are produced, and we know but little of that property. The explosive action in a gas engine produces not only the mechanical force we desire, but also a quantity of heat we do not want, and at a cost of a portion of the gas. In a similar manner, in the steam-engine the largest portion of the heat of the coal is converted into forces which are lost; a large amount of it is uselessly expended in warming the machine itself and the surrounding atmosphere; much also is lost by friction. That "knowledge is power" is an old maxim, but that _new knowledge is new power_ is a new maxim {23} which scientific discovery has impressed upon us. By means of discoveries we have acquired new powers; by those of electricity we have acquired the ability of conversing with each other at unlimited distances, and by means of those in optics we are enabled to analyse the composition, and perceive some of the physical changes of the most distant heavenly bodies. As our ignorance is probably much greater than our knowledge, more inventions also, and extensions of human power, must ultimately result from discovering new qualities of bodies, than by applying to useful purposes their already known properties. Experience in science has already shown that it is by means of invention based upon _new_ discoveries that the greatest utilities are obtained, rather than by the exercise of invention upon knowledge acquired long ago. The information obtained by research in former times has been largely exhausted for the purposes of invention by modern inventors, and what we very greatly require now is _new_ knowledge. Experience in science also leads us to believe that the extent of possible discovery is as boundless as Nature, and that an immense amount of new knowledge may yet be discovered. Every discoverer of repute could supply a copious list of investigations yet to be made.