354 SPECIAL RESULTS IN THE XJRANOLOGICAL 



of Pisa and Pavia, witnessed these experiments, the results 

 of which varied according to the Moon's age and altitude. 

 To what amount, expressed in fractional parts of the centi 

 grade thermometer, the increase of temperature produced in 

 Melloiii's thermoscopic pile corresponded, had not then (in 

 the summer of 1846) been examined ( 565 ). 



The ashy grey light seen on the Moon's disk, when 

 for some days before and after the new moon the part 

 illuminated by the Sun is only a narrow bow, is earthlight 

 on the Moon " the reflection of a reflection." The less 

 the Moon appears illuminated as viewed from the Earth, 

 the more illuminated is the Earth as viewed from the 

 Moon. But the earthlight received on the Moon is 

 13J- times stronger than the moonlight received on the 

 Earth, and is bright enough to be perceived by us on a 

 second reflection. In this faint light the telescope can dis- 

 tinguish both the larger spots, and also bright shining 

 points mountain- summits in the lunar landscapes; and, 

 even when more than half the Mo'on's disk reflects to us the 

 full illumination of the Sun, a faint grey light can still be 

 seen on the remaining portion by the aid of the telescope 

 ( 566 ). These phenomena are particularly striking when 

 viewed from the high mountain plateaus of Quito and 

 Mexico. Since Lambert's and Schroter's writings, the opi- 

 nion has prevailed, that the very various degrees of intensity 

 of the grey light of the Moon at different times proceed from 

 the stronger or fainter return of the solar light from the sur- 

 face of the Earth, according as this is reflected from connected 

 continental masses full of sandy or rocky deserts, grassy 

 steppes, and tropical forests, or from extensive oceanic sur- 

 faces. . Lambert, on the ]4th of Eebruary, 1774, made, 



