It is not highly necessary after what has been already said in these pages, to adduce much evidence to show that scientific discoveries, either directly or through the medium of the inventions based upon them, have been a great cause of mental and moral progress. As however there are many persons who do not perceive the dependence of such progress, and especially of moral advance, upon science, a few of the chief relations of those subjects to each other may be pointed out. The dependence of mental progress upon science may be rendered manifest in several ways:--1st. By showing that new scientific knowledge is continually extending and modifying our views of existing things. 2nd. That inventions based upon scientific discoveries have aided and extended our mental powers:--3rd. That mental phenomena may be made the subject of experiment, observation, analysis, and {84} inference:--4th. That the criteria of truth, and the mental powers and processes employed for discovering and detecting truth, are the same in mental as in physical science, and, 5th. That mental action is subject to the great principles and laws of science. And moral progress may be proved to have a scientific basis:--1st. By shewing that moral actions are a class of mental actions, and therefore subject to the same fundamental laws and influences:--2nd. That the discovery of new scientific knowledge, and the use of inventions based upon it, often conduce to morality:--3rd. That moral phenomena may be made the subject of experiment, observation, analysis, and inference:--4th. That the criteria of truth, and the mental faculties and processes employed, in discovering truth, are the same in moral as in physical science:--5th. That the fundamental rules of morality are subject to the great principles of science:--6th. That moral improvement follows in the wake of scientific advance:--and 7th. By showing the moral influence of experimental research in imparting "the scientific spirit;" promoting a love of truth; dispelling ignorance and superstition; detecting error; imparting certainty and accuracy to our knowledge; inculcating obedience to law; producing uniformity of belief; aiding economy and cleanliness, promoting humanity, &c, &c. Each of these will be treated with extreme brevity. MENTAL PROGRESS. The chief object of this chapter is only to shew {85} that mental action is largely consistent with the great principles of science; not that in our present state of knowledge, mental phenomena can be entirely explained by them, or that mental actions involve nothing more than physical and chemical processes.