104 



draw from the isle of TenerifFe, the Piton or Su- 

 gar Loaf is seen for a long time in a positive man- 

 ner, because it reflects a whitish light, and clear- 

 ly detaches itself from the sky ; but as this cone 

 is only 80 toises high, by 40 in breadth at it's sum- 

 mit, it has recently been a question*, whether 

 from the diminutiveness of it's mass it can be vi- 

 sible at distances which exceed 40 leagues ; and 

 if it be not rather probable, that navigators dis- 

 tinguish the peak as a small cloud above the ho- 

 rizon, only when the base of the Piton begins to 

 be visible on it. If we admit, that the mean 

 breadth of the Sugar Loaf is 100 toises, we find 

 that the little cone, at 40 leagues distance, still 

 subtends, in the horizontal direction, an angle of 

 more than three minutes. This angle is consi- 

 derable enough to render an object visible ; and 

 if the height of the Piton greatly exceeded it's 

 basis, the angle in the horizontal direction might 

 be still smaller, and the object still continue to 

 make an impression on our organs; for microme- 

 trical observations have proved, that the limit of 

 vision is but a minute only, when the dimensions 

 of the objects are the same in every direction. 

 We distinguish at a distance, by the eye only, 

 trunks of trees insulated in a vast plain, though 



become perceptible to our organs, and the mountain detach 

 itself distinctly from the sky, that one of these lights should 

 be a sixtieth part stronger than the other. 



* Marchand. t. 2, p. 10. 



