same time, also, he discovered in the field of view, two complete images of the ship in the air, vertical to the ship itself, one being inverted and the other erect, having their bulls joined." As the ship receded from the shore, less and less of its masts became visible, and as it descended the images ascended; but as the ship did not sink below the horizon, Dr. Vince did not observe at what time and in what order the images vanished.

The alterations of the refractive power may arise partly from the variations of its density, and partly from the variations of its moisture; and the passage of the rays through the boundary of the fog may there suffer a very considerable refraction; for, from the motion of the fog, and that of the images above-mentioned, Dr. Vince had no doubt that the fog was a very considerable agent in producing the phenomena. When all the causes co-ope rate, we can easily perceive that they may produce the effects which he has descibed.

One of the most extraordinary phenomena produced by unusual refraction, was observed by Dr. Vince at Ramsgate on the 6th August, 1808, about 7h. P. M. Between Ramsgate and Dover there is a hill, over which the tops of the four turrets of Dover Castle are usually seen to a person at Ramsgate. At the time above mentioned, however, Dr. Vince, when at Ramgate, not only saw the four turrets, but the whole of the castle, appearing as if it were situated on the side of the hill next to Ramsgate, and rising as much above the hill as usual, as if it had been brought over and placed on the Ramsgate side of the hill. This appearance continued about twenty minutes. Between Ramsgate, and the land from which the hill rises, there is about six miles of sea, and from thence to the top of the hill about the same distance, the height of the eye above the surface of the sea being about seventy feet. is a very singular circumstance in this phenomenon, that the image of the castle was so very strong and well defi ned that the hill itself did not appear through the image.

It

In all the preceding cases of unusual refraction, the difference of density in the air has been related to a horizontal line, and consequently the different images have been situated in the same vertical line. A very curious ease, however, of a lateral mirage was observed at Geneva,jon

the 17th Sept. 1818, at 10 o'clock P. M. by MM. Jurine and Soret. A bark near Bellerive, at the distance of about 1000 toises, was seen approaching to Geneva by the left bank of the lake, and at the same time an image of the sails was observed above the water, which, instead of following the direction of the bark, separated from it, and appeared to approach (ieneva by the right bank of the lake, the image moving from east to west, while the bark moved from north to south. When the image separated from the bark it was of the same dimensions as the bark, but it diminished as it receded from it, so as to be redueed to one-half when the phenomenou ceased. In this ease of unusual refraction the plane of refraction was clearly horizontal; and consequently the two masses of air of different density must have been laterally contiguous to each other.

THE following accounts of Optical Illusions arising from at. mospheric refraction are from the Journal of Capt. Scoresby in a voyage to the polar seas in 1822.

On the 7th of June, such finely marked ice-blinks appeared in the atmosphere, in connexion with the horizon, as to present a perfect map of all the ice and openings of water for twenty or thirty miles around.

“The reflection was so strong and definite, that I could readily determine the figure and probable extent of all the fields and floes within this limit, and could distinguish packed or open ice, by its duller and less yellow image; while every vein and lake of water, producing its marked reflection by a deep blue, or bluish-black patch, amid the ice-blinks, enabled me to ascertain where the most was ter lay, and the nature of the obstacles that intervened. By this means only, I discovered a large opening immediately to the north-westward of the lake we had so long navigated, with a considerable expanse in the same direction, at a greater distance, bounded by sheets of ice that appeared to be of prodigious magnitude. This induced me to examine the ice very closely in this quarter, when, in the very spot marked by the blink as being the narrowest, ice was found to be in the act of opening, so as to per

mit our passing through towards the north-west. At the extremity of the first opening, or lake, there was a compact barrier of floes, wherein, however, after a few hours detention, we discovered a narrow dubious channel, that eventually conducted us into the expanse of water pointed out by reflection in the atmosphere."

The

"The strong action of the sun's rays soon produced such an unequal density in the atmopshere, that some of the most extraordinary phenomena to which this cireumstance gives rise were exhibited. The land, to appearance, was suddenly brought fifteen or twenty miles nearer to us; its boldness and clearness, as seen from the deck, being superior to what its elevation and distinctness had previously been as seen from the mast-head. The ice about the horizon assumed various singular forms:hummocks became vertical columns; floes and fields arose above the horizon, like cliffs of prismatic-formed spar and, in many places, the ice was reflected in the atmosphere at some minutes elevation above the horizon. ships around us, consisting of eight or nine sail, presented extraordinary characters. Their sails and masts were strangely distorted. Sometimes the courses would be de- pressed to almost nothing; the topsails expanded to near four times their proper height, and the topgallant-sails truncated. Occasionally a very odd spectacle occurred; an additional sail appeared above the topgallant-sail, like a royal hanging loose; and sometimes the expanded topsail, divided into two distinct sails, by the separation of all the additional height given by the refraction, which, slowly rolling upward, as it were, like the lifting of a curtain, dispersed, and became invisible, after leav ing the mast-head. Above some distant ships, there was an inverted image in the air, many times larger than the object itself: this, in some instances, was at a considerable elevation above the ship; but it was found to be of a less size whenever the original and the image were not in contact. The image of one ship was distinetly seen for several minutes together, though the object to which it referred was not in sight! One ship was crowned with two images; the first an inverted one, and the second, a circumstance I never before observed, in its proper position. Altogether, the shipping, and other objects around. us, presented a most amusing spectacle. They were per

petually changing their appearance, and afforded me abundant entertainment for hours together. The most remarkable effect produced, was on the most distant objeets, the interesting appearances of which not being discernible without the use of a telescope, probably escaped general observation."

"The most extraordinary effect of this state of the at mosphere, however, was the distinct inverted image of a ship in the clear sky, over the middle of the large bay or inlet before mentioned,-the ship itself being entirely beyond the horizon. Appearances of this kind I have be fore noticed, but the peculiarities of this were,-the perfection of the image, and the great distance of the vessel that it represented. It was so extremely well defined, that when examined with a telescope by Dollond, I could distinguish every sail, the general" rig of the ship," and its particular character; insomuch that I confidently pro nounced it to be my father's ship, the Fame, whieh it afterwards proved to be;-though, on comparing notes with my father, I found that our relative position at the time gave our distance from one another very nearly thirty miles, being about seventeen miles beyond the ho rizon, and some leagues beyond the limit of direct vision. I was so struck by the peculiarity of the circumstance, that I mentioned it to the officer of the watch, stating my full conviction that the Fame was then eruizing in the neighbouring inlet.”

MR. EDITOR,

FOR THE MONITOR.

1 Understand that the Sabbath Schools in the City of Boston are to be continued through the winter. It gratifies me much to hear this. Some selfdenial it may require on the part of the superintendents and teachers; but it is believed they will find their reward in the improvement of their pupils. The practice of suspending these schools during the season of winter is of dangerous tendency, and appears to me inexpedient and unnecessary. I speak now of Sabbath Schools generally. If they are importaut in summer, they are also in winter. Nothing, as I conceive, is gained by an intermission of the exercises;

The pupils return in the spring to their lessons with no new impalse; but rather with aversion. Fond of ease and leisure, impatient of toil and restraint, the relaxation weds their young hearts to indolence, unnerves them for vigorous efforts, the benefit of which they cannot be supposed fully to perceive.-Besides, what time more suitable is there for learning scripture than the long evenings of winter. If instead of the mirth, the sports and games, the senseless chit chat and pernicious reading which too often beguile these evenings of their tediousness, a part of them should be spent in literary and historical and scientific research, and another part in studying the precious volume of divine truth whieh is able to save them that understand and love it; if only a small proportion of each evening were thus employed, the acquisitions would not be inconsiderable-acquisitions which would place the youth who makes them at a laudable, perhaps unattainable eminence above his fellows. He would be able, at the return of spring, to meditate a bolder and loftier flight in the knowledge of men and things, and of the infinite God, than they could hope to attain. The habit of diligence and the love of knowledge, which would be acquired or confirmed by the discipline I propose, might be even more valuable than the acquisitions themselves.

1

But I need not dwell on the importance of continuing Sabbath Schools during the winter.

Is it not practicable? In some places it probably is not. Meeting-houses, in which the school has usually recited, contain no stoves, and are too cold to be convenient. In many towns, however, the people have learned, what all know, that it is as agreeable to be warm on the Sabbath as on other days, and have furnished means for readering their house of worship comfortable. In others they assemble in buildings, which are occupied and kept warm during the week, and which with trifling expense may be warmed on the Sabbath. And, indeed, it can be no very difficult thing to provide a suitable house in every place. The object is sufficiently important to demand the erection of stoves in each meeting house, for the convenience of a school, even if nothing else could be urged in favour of such a measure.

It may perhaps be further objeeted, that the intermission is too short to afford time for the recitations. I can