CHAPTER VII. _Illusions._--Reality and appearance--Preconceived

impressions--Deception by sunlight--Distorted forms and colors--Changed appearance of mountains--Changes in line and light--False perspective--Abnormal foreshortening--Contradictions and denials--Deceptive distances--Dangers of the desert--Immensity of valley-plains--Shadow illusions--Color-patches on mountains--Illusions of lava-beds--Appearance of cloud-shadows--Mirage--Need of explanation--Refraction of light-rays--Dense air-strata--Illustration of camera-lens--Bent light-rays--Ships at sea and upside down--Wherein the illusion--“Looming” of vessels, cities, and islands--Reversed image of mountains--Horses and cattle in mirage--Illusion of rising buttes--Other causes of mirage--Water-mirage--The lake appearance--How produced--Objects in water--Confused mirage--The swimming wolf--Colors and shadows in mirage--Trembling air--Beauty of mirage 109