NATURAL PHILOSOPHY. 153 



of the warm and cold air, and thus a screen is produced on which the 

 objects reflected from below are seen as i:i a mirror. Meanwhile, by 

 refraction, this image is seen higher up than it is really painted on 

 the mist. This was obviously the cause of the strange phantoms 

 which we have witnessed on Lake Superior. It is no uncommon 

 thing on other parts of the Lake to see vessels inverted in the air be- 

 fore their hulls become visible above the horizon ; and it is well known 

 that similar appearances very rarely occur on our sea-coast, and have 

 given rise, in former times, to strange and superstitious tales." 



Prof. Agassiz mentioned an additional phenomenon, which was 

 frequently witnessed by himself and his party upon Lake Superior. 

 Not only did the shores and islands, with all their vegetation, appear 

 repeated, higher up and in an inverted position, but above this invert- 

 ed landscape there was sometimes still another, in which every thing 

 was upright, so that the picture was twice repeated above the surface 

 of real nature, once inverted, and above that, the same erect. This 

 fact must be explained by any theory which professes to account,for 

 similar phenomena ; but it may be simply the image of the landscape, 

 inverted upon the surface of the lake, reproduced with the inverted 

 image of the landscape itself. 



HEAT AND EVAPORATION OF THE EARTH. 



AT a recent meeting of the Geographical Society of Bombay, Mr. 

 G. Buist made an interesting communication on a method adopted by 

 him for ascertaining the heat of, and evaporation from, the soil. The 

 objects and details of the experiment are stated to be as follows : 

 " As the evaporation from a shallow dish of water exposed to the sun, 

 and liable to be raised to a temperature of 100, or 120, gives no 

 idea of the amount of evaporation from the surface of the sea, large 

 pools, or lakes, which vary very little in temperature, he was anxious 

 to determine the amount of evaporation from the surface of wet 

 earth, compared with that from the surface of a considerable mass of 

 water. With this view, two zinc cylinders were prepared, three feet 

 long and four inches in diameter, and secured by a strong brass ring, 

 at the top and bottom, carefully turned. These contained fifteen 

 pounds, or a gallon and a half of water, each, temperature 82, or 

 nineteen pounds of the loose red earth to be found associated with 

 trap-rock. When filled with earth well shaken down, they were able 

 to take in six and a half pounds of water to overflowing. Each was 

 provided with a glass tube, of a quarter of an inch bore, connected 

 with the bottom of a cylinder, and running parallel with it, to the 

 top ; this was intended to show^how high the water stood inside. On 

 filling one of them with earth,' and then adding water till it flowed 



^y * ^j 



over, that in the tube decreased of course rapidly by evaporation, 

 but, strange to tell, after continuing to descend from noon till day- 

 break, it commenced immediately to rise again till 11 A. M., remain- 

 ed motionless till 1 P. M., when it began to sink, and so continued 

 descending, till about an hour after sunrise, when it commenced im- 

 mediately to rise, and so continued till the same hour as during the 



