Curiosities of Science. 31 



to the figure or fluttered in the breeze, and judging from the known 

 distance, the angle at which the moving object could be distinctly seen 

 varied from 7" to 12". White objects on a black ground are, according 

 to Hueck, distinguished at a greater distance than black objects on a 

 white ground. 



Gauss's heliotrope light has been seen with the naked eye reflected 

 from the Brocken on Hobenhagen at a distance of about 227,000 feet, 

 or more than 42 miles ; being frequently visible at points in which the 

 apparent breadth of a three-inch mirror was only 0"'43. 



THE SMALLEST BRIGHT BODIES. 



Ehrenberg has found from experiments on the dust of dia- 

 monds, that a diamond superficies of Tro^h of a line in diameter 

 presents a much more vivid light to the naked eye than one of 

 quicksilver of the same diameter. On pressing small globules 

 of quicksilver on a glass micrometer, he easily obtained smaller 

 globules of the T <3c>th to the ^o^th of a line in diameter. In 

 the sunshine he could only discern the reflection of light, and 

 the existence of such globules as were ^th of a line in dia- 

 meter, with the naked eye. Smaller ones did not affect his 

 eye ; but he remarked that the actual bright part of the glo- 

 bule did not amount to more than no-oth of a line in diameter. 

 Spider threads of a^th m diameter were still discernible 

 from their lustre. Ehrenberg concludes that there are in or- 

 ganic bodies magnitudes capable of direct proof which are in 

 diameter Too ' 00() of a line ; and others, that can be indirectly 

 proved, which may be less than a six-millionth part of a Paris- 

 ian line in diameter. 



VELOCITY OF LIGHT. 



It is scarcely possible so to strain the imagination as to con- 

 ceive the Velocity with which Light travels. " What mere 

 assertion will make any man believe," asks Sir John Herschel, 

 " that in one second of time, in one beat of the pendulum of 

 a clock, a ray of light travels over 192,000 miles; and would 

 therefore perform the tour of the world in about the same time 

 that it requires to wink with our eyelids, and in much less time 

 than a swift runner occupies in taking a single stride 1 ?" Were 

 a cannon-ball shot directly towards the sun, and were it to main- 

 tain its full speed, it would be twenty years in reaching it; and 

 yet light travels through this space in seven or eight minutes. 



The result given in the Annuaire for 1842 for the velocity 

 of light in a second is 77,000 leagues, which corresponds to 

 215,834 miles ; while that obtained at the Pulkowa Observatory 

 is 189,746 miles. William Richardson gives as the result of the 

 passage of light from the sun to the earth 8' 19" '28, from which 

 we obtain a velocity of 215,392 miles in a second. Memoirs of 

 the Astronomical Society ', vol. iv. 



