Curiosities of Science. 



heaps ; and that all the weight which the bottom of the tube 

 sustains is only that of the heap which first falls upon it, as 

 the succeeding heaps do not press downward, but only against 

 the sides or walls of the tube. 



FIGURE OF THE EARTH. 



By means of a purely astronomical determination, based 

 upon the action which the earth exerts on the motion of the 

 moon, or, in other words, on the inequalities in lunar longi- 

 tudes and latitudes, Laplace has shown in one single result the 

 mean Figure of the Earth. 



It is very remarkable that an astronomer, without leaving his obser- 

 vatory, may, merely by comparing his observations with mean analytical 

 results, not only be enabled to determine with exactness the size and 

 degree of ellipticity of the earth, but also its distance from the sun and 

 moon ; results that otherwise could only be arrived at by long and ar- 

 duous expeditions to the most remote parts of both hemispheres. The 

 moon may therefore, by the observation of its movements, render ap- 

 preciable to the higher departments of astronomy the ellipticity of the 

 earth, as it taught the early astronomers the rotundity of our earth by 

 means of its eclipses. Laplace's Expos, du Syst. du Monde. 



HOW TO ASCERTAIN THE EARTH'S MAGNITUDE. 



Sir John Herschel gives the following means of approxima- 

 tion. It appears by observation that two points, each ten feet 

 above the surface, cease to be visible from each other over still 

 water, and, in average atmospheric circumstances, at a distance 

 of about eight miles. But 10 feet is the 528th part of a mile ; 

 so that half their distance, or four miles, is to the height of 

 each as 4 x 528, or 2112:1, and therefore in the same propor- 

 tion to four miles is the length of the earth's diameter. It 

 must, therefore, be equal to 4x2112=8448, or in round num- 

 bers, about 8000 miles, which is not very far from the truth. 



The excess is, however, about 100 miles, or s^th part. As convenient 

 numbers to remember, the reader may bear in mind, that in our latitude 

 there are just as many thousands of feet in a degree of the meridian as 

 there are days in the j^ear (365) ; that, speaking loosely, a degree is 

 about seventy British statute miles, and a second about 100 feet ; that 

 the equatorial circumference of the earth is a little less than 25,000 

 miles (24,899), and the ellipticity or polar flattening amounts to ^th 

 part of the diameter. Outlines of Astronomy. 



MASS AND DENSITY OF THE EARTH. 



With regard to the determination of the Mass and Density 

 of the Earth by direct experiment, we have, in addition to the 

 deviations of the pendulum produced by mountain masses, the 

 variation of the same instruments when placed in a mine 1200 

 feet in depth. The most recent experiments were conducted 



