The discussion above referred to turns on the question: Do states of consciousness enter as links into the chain of antecedence and sequence, which give rise to bodily actions, and to other states of consciousness; or are they merely by-products, which are not essential to the physical processes going on in the brain? Speaking for myself, it is certain that I have no power of imagining states of consciousness, interposed between the molecules of the brain, and influencing the transference of motion among the molecules. The thought 'eludes all mental presentation; and hence the logic seems of iron strength which claims for the brain an automatic action, uninfluenced by states of consciousness. But it is, I believe, admitted by those who hold the automaton-theory, that states of consciousness are produced by the marshalling of the molecules of the brain; and this production of consciousness by molecular motion is to me quite as unthinkable as the production of molecular motion by consciousness. If, therefore, unthinkability be the proper test, I must equally reject both classes of phenomena. I, however, reject neither, and thus stand in the presence of two Incomprehensibles, instead of one Incomprehensible. While accepting fearlessly the facts of materialism dwelt upon in these pages, I bow my head in the dust before that mystery of mind, which has hitherto defied its own penetrative power, and which may ultimately resolve itself into a demonstrable impossibility of self-penetration.

But the secret is an open one-the practical monitions are plain enough, which declare that on our dealings with matter depends our weal or woe, physical and moral. The state of mind which rebels against the recognition of the claims of materialism' is not unknown to me. I can remember a time when I regarded my body as a weed, so much more highly did I prize the conscious strength and pleasure derived from moral and religious feeling

-which, I may add, was mine without the intervention of dogma. The error was not an ignoble one, but this did not save it from the penalty attached to error. Saner knowledge taught me that the body is no weed, and that if it were treated as such it would infallibly avenge itself. Am I personally lowered by this change of front? Not so. Give me their health, and there is no spiritual experience of those earlier years no resolve of duty, or work of mercy, no act of self-renouncement, no solemnity of thought, no joy in the life and aspects of nature-that would not still be mine; and this without the least reference or regard to any purely personal reward or punishment looming in the future.

expansiveness,' both he

As I close these remarks, the latest utterances of the Bishop of Peterborough reach me. I observe with regret that, notwithstanding all their and his Right Rev. Brother of Manchester, appear to know almost as little of the things which belong to our peace, as that frenzied ritualist who, a day or two ago, raised the cry of excommunicated heretic!' against the Bishop of Natal. Happily we have amongst us our Jowetts and our Stanleys, not to mention other brave men, who see more clearly the character and magnitude of the coming struggle; and who believe undoubtingly that out of it the truths of science will emerge with healing in their wings.

And now I have to utter a farewell' free from bitterness to all my readers; thanking my friends for a sympathy more steadfast, I would fain believe, if less noisy, than the antipathy of my foes; and commending to these a passage from Bishop Butler, which they have either not read or failed to lay to heart. 'It seems,' saith the Bishop, that men would be strangely headstrong and self-willed, and disposed to exert themselves with an impetuosity which would render society insupportable,

and the living in it impracticable, were it not for some acquired moderation and self-government, some aptitude and readiness in restraining themselves, and concealing their sense of things.' In temperance of language, at least, his Grace the Archbishop of Canterbury has set a good example.'

ATHENEUM CLUB:

December 5, 1874.

JOHN TYNDALL.

A still more remarkable illustration of absence of vituperation, associated with real scientific insight, is furnished by the sermon of the Bishop of Carlisle, reported in the 'Oxford University Herald' for November 28, 1874. To Dr. Quarry, and to a contributor in the current number of the British Quarterly Review,' my special acknowledgments are due. (November, 1875.)

A

VIII.

CRYSTALS AND MOLECULAR FORCE.

FEW

1874.

years ago I paid a visit to a large school in the country, and was asked by the principal to give a lesson to one of the classes. I agreed to do so, provided he would let me have the youngest boys in his school. To this he willingly assented: and, after casting about in my mind as to what could be said to the little fellows, I went to a village hard by and brought some sugarcandy. This was my teaching apparatus. The boys having assembled, I began by describing the way in which sugar-candy and other artificial crystals are formed, and tried to place vividly before their young minds the architectural process by which crystals are built up. They listened to me with eager interest. I examined the

crystal before them, pointing out its various faces and angles; and when they found that in a certain direction it could be split into thin lamina with shining surfaces of cleavage, their joy was at its height. They had no notion that the thing they had been crunching and sucking all their lives, embraced so many hidden points of beauty. I spent a very pleasant hour with these young philosophers; and at the end of the lesson emptied my pockets among the class, and permitted them to experiment upon the sugar-candy in the way usual to boys.

I know not whether this great assembly will deem it

an impertinence on my part if I seek to instruct them, for an hour or so, on the subject chosen for my class. In doing so I run the imminent risk of being wearisome as well as impertinent; while labouring under the further disadvantage of not being able to make matters pleasant at the conclusion of the lecture, by the process adopted at the end of my lesson to the boys. The experiment, however, must be made.

We are to consider this evening some of the phenomena of Crystallisation; but in order to trace the genesis of the notions now entertained upon the subject, we have to go a long way back. In the drawing of a bow, the darting of a javelin, the throwing of a stone--in the lifting of burdens, and in personal combats, even savage man became acquainted with the operation of force. His first efforts were directed towards securing food and shelter; but ages of discipline, during which his power was directed against nature, against his prey, and against his fellow-man, taught him foresight. He laid by at the proper season stores of food, thus obtaining time to look about him, and to become an observer and enquirer. He discovered two things, which must have profoundly stirred his curiosity, and sent down to us the record of his discovery. He found that a kind of resin dropped from a certain tree possessed, when rubbed, the power of drawing light bodies to itself, and of causing them to cling to it; and he also found that a particular stone exerted a similar power over a particular kind of metal. I allude, of course, to electrified amber, and to the loadstone, or natural magnet, and its power to attract particles of iron. Previous experience had enabled our early enquirer to distinguish between a push and a pull. In fact, muscular efforts might be divided into pushes and pulls. Augmented experience showed him that in the case of the magnet and the amber, pulls and pushes—