MEASUREMENT OF DISTANCES. 41 



circle, the number of degrees subtended by a distant object, 

 as a church, at A C, and let this angle be two degrees ; we have 

 here a triangle A- B C, and knowing its angles, and any one 

 side, we can determine the other sides. Suppose we know 

 the side B C, or the distance of the Church, to be 1 mile, we 

 can ascertain the height A C thus : Twice B C, or 2 miles, 

 will be the diameter of a circle whose centre is the eye of the 

 spectator, and whose radius, the distance of the Church. Three 

 times this (nearly), or 6 miles, will be the whole circumference, 

 and six miles divided by 360 will give the length of one degree, 

 and twice this, since the angle A B C is 2 degrees, will give 

 the height A C. Allowing 5000 feet to the mile, 6 miles would 

 be 30,000 feet, and this divided*by 360, gives 83J feet for the length 

 of one degree, consequently 2 degrees are 166 feet, which is the 

 height required. Now in any triangle whatever, we can deter- 

 mine the length of all its sides, provided the length of 'one side is 

 given and also the angles. We do not mean to be understood 

 that this is the actual process employed by astronomers to deter- 

 mine the distance of the moon, and other heavenly bodies, but 

 simply introduce it as an explanation of the principle. 



By means of parallax, the distance from the moon to the earth 

 has been ascertained to be 60 semi-diameters of the latter, and the 

 distance of the earth from the sun has been determined 

 to be 95,000,000 of miles. When we reflect upon this 

 vast distance, the absurdity of that system which denied to 

 the earth a revolution on its axis, once in 24 hours, is striking- 

 ly apparent. We could not conceive of the amazing velocity 

 with which the sun must move, at the immense distance 

 which it is situated from the earth, if it was obliged to 

 travel once around in 24 hours. It would require a rate of about 

 24,000,000 miles per hour, or 400,000 miles in one minute, 

 and 6,666 miles each tick of the clock. Such velocity is abso- 

 lutely incredible, and this would be to save our little globe from 

 turning on its axis at the rate of 1000 miles an hour, or about 17 

 miles in one minute. When the distance of any of the heavenly 

 bddies becomes known, its actual diameter in miles-can be easily 

 ascertained. It is no more difficult to obtain the diameter of the 



