Curiosities of Science. 103 



tolerably well in stating that " they have never seen stars by 

 day, but that when observed at night through deep shafts, the 

 sky appeared quite near, and the stars larger." Saussure states 

 that stars have been seen with the naked eye in broad day- 

 light, on the declivity of Mont Blanc, at an elevation of 12,757 

 feet, as he was assured by several of the alpine guides. The 

 observer must be placed entirely in the shade, and have a thick 

 and massive shade above his head, else the stronger light of 

 the air will disperse the faint image of the stars ; these condi- 

 tions resembling those presented by the cisterns of the ancients, 

 and the chimneys above referred to. Humboldt, however, 

 questions the accuracy of these evidences, adding that in the 

 Cordilleras of Mexico, Quito, and Peru, at elevations of 15,000 

 or 16,000 feet above the sea-level, he never could distinguish 

 stars by daylight. Yet, under the ethereally pure sky of Cu- 

 maua, in the plains near the sea-shore, Humboldt has fre- 

 quently been able, after observing an eclipse of Jupiter's sa- 

 tellites, to find the planet again with the naked eye, and has 

 most distinctly seen it when the sun's disc was from 18 to 20 

 above the horizon. 



LOST HEAT OF THE SUN. 



By the nature of our atmosphere, we are protected from 

 the influence of the full flood of solar heat. The absorption 

 of caloric by the air has been calculated at about one-fifth of 

 the whole in passing through a column of 6000 feet, estimated 

 near the earth's surface. And we are enabled, knowing the 

 increasing rarity of the upper regions of our gaseous envelope, 

 in which the absorption is constantly diminishing, to prove 

 that about one-third of the solar heat is lost by vertical trans- 

 mission through the whole extent of our atmosphere. J. D. 

 Forbes, F.R.S. ; Bakerian Lecture, 1842. 



THE LONDON MONUMENT USED AS AN OBSERVATORY. 



Soon after the completion of the Monument on Fish Street 

 Hill, by Wren, in 1677, it was used by Hooke and other mem- 

 bers of the Royal Society for astronomical purposes, but aban- 

 doned on account of the vibrations being too great for the 

 nicety required in their observations. Hence arose the report 

 that the Monument was unsafe, which has been revived in our 

 time ; " but," says Elmes, " its scientific construction may bid 

 defiance to the attacks of all but earthquakes for centuries to 

 come." This vibration in lofty columns is not uncommon. 

 Captain Smythe, in his Cycle of Celestial^ Objects, tells us, that 

 when taking observations on the summit of Pompey's Pillar, 

 near Alexandria, the mercury was sensibly affected by tremor, 

 although the pillar is a solid. 



