But I did not devote myself altogether to experiments. Exercise is as necessary for the body as the mind. Without full health a man cannot enjoy comfort, nor can he possess endurance. I therefore took plenty of exercise out of doors. I accompanied my father in his walks round Edinburgh. My intellect was kept alive during these delightful excursions. For sometimes my father was accompanied by brother- artists, whose conversation is always so attractive; and sometimes by scientific men, such as Sir James Hall, Professor Leslie, Dr. Brewster, and others. Whatever may have been my opportunities for education so-called, nothing could have better served the purpose of real education (the evolution of the mental faculties) than the opportunities I enjoyed while accompanying and listening to the conversation of men distinguished for their originality of thought and their high intellectual capacity. This was a mental culture of the best kind.

The volcanic origin of the beautiful scenery round Edinburgh was often the subject of their conversation. Probably few visitors are aware that all those remarkable eminences, which give to the city and its surroundings so peculiar and romantic an aspect, are the results of the operation, during inconceivably remote ages, of volcanic force penetrating the earth's crust by disruptive power, and pouring forth streams of molten lava, now shrunk and cooled into volcanic rock. The observant eye, opened by the light of Science, can see unmistakable evidences of a condition of things which were in action at periods so remote as, in comparison, to shrink up the oldest of human records into events of yesterday.

I had often the privilege of standing by and hearing the philosophic Leslie, Brewster, and Hall, discussing these volcanic remains in their actual presence; sometimes at Arthur's Seat or on the Calton Hill, or at the rock on which Edinburgh Castle stands, Their observations sank indelibly into my memory, and gave me the key to the origin of this grand class of terrestrial phenomena. When standing at the "Giant's Ribs," on the south side of Arthur's Seat, I felt as if one of the grandest pages of the earth's history lay open before me. The evidences of similar volcanic action abound in many other places near Edinburgh; and they may be traced right across Scotland from the Bass Rock to Fingal's Cave, the Giant's Causeway in Antrim, and Slievh League on the south-west coast of Donegal in Ireland.

Volcanic action, in some inconceivably remote period of the earth's crust history, has been the Plough, and after denudation by water, has been the Harrow, by which the originally deep-seated mineral treasures of the globe have been brought within the reach of man's industrial efforts. It has thus yielded him inexhaustible mineral harvests, and helped him to some of the most important material elements in his progress towards civilisation. It is from this consideration that, while enjoying the results of these grand fundamental actions of the Creator's mighty agencies in their picturesque aspect, the knowledge of their useful results to man adds vastly to the grandeur of the contemplation of their aspect and nature. This great subject caused me, even at this early period of my life, to behold with special interest the first peep at the structure of the moon's surface, as revealed to me by an excellent Ramsden "spy-glass," which my father possessed, and thus planted the seed of that earnest desire to scrutinise more minutely the moon's wonderful surface, which in after years I pursued by means of the powerful reflecting telescopes constructed by myself.

To turn to another subject. In 1822 the loyalty of Scotland was greatly excited when George the Fourth paid his well-known visit to Edinburgh. It was then the second greatest city in the kingdom, and had not been visited by royalty for about 170 years. The civic authorities, and the inhabitants generally, exerted themselves to the utmost to give the king a cordial welcome, in spite of a certain feeling of dissatisfaction as to his personal character. The recent trial and death of Queen Caroline had not been forgotten, yet all such recollections were suppressed in the earnest desire to show every respect to the royal visitor. Edinburgh was crowded with people from all parts of the country; heather was arrayed on every bonnet and hat; and the reception was on the whole magnificent. Perhaps the most impressive spectacle was the orderliness of the multitude, all arrayed in their Sunday clothes. The streets, windows; and house- tops were crowded; and the Calton Hill, Salisbury Crags, and even Arthur's Seat it self, were covered with people. On the night before the arrival a gigantic bonfire on Arthur's Seat lit up with a tremendous blaze the whole city, as well as the surrounding country. It formed a magnificent and picturesque sight, illuminating the adjacent mountains as well as the prominent features of the city. It made one imagine