Curiosities of Science. 79 



of a Centauri, and its parallax only 0'15". This, in effect, as- 

 cribes to it an intrinsic splendour equal to 96'63 times that of 

 a Centauri, and therefore 224' 7 times that of our sun." 



This is justly regarded as one of the most brilliant triumphs 

 of astronomical science, for the delicacy of the investigation is 

 almost inconceivable ; yet the reasoning is as unimpeachable 

 as the demonstration of a theorem of Euclid. 



LIGHT OF A STAE SIXTEENFOLD THAT OF THE SUN. 



The bright star in the constellation of the Lyre, termed 

 Vega, is the brightest in the northern hemisphere ; and the com- 

 bined researches of Struve, father and son, have found that 

 the distance of this star from the earth is no less than 130 bil- 

 lions of miles ! Light travelling at the rate of 192 thousand 

 miles in a second consequently occupies twenty-one years in 

 passing from this star to the earth. Now it has been found, 

 by comparing the light of Vega with the light of the sun, that 

 if the latter were removed to the distance of 130 billions of 

 miles, his apparent brightness would not amount to more than 

 the sixteenth part of the apparent brightness of Vega. We 

 are therefore warranted in concluding that the light of Vega 

 is equal to that of sixteen suns. 



DIVERSITIES OF THE PLANETS. 



In illustration of the great diversity of the physical peculi- 

 arities and probable condition of the planets, Sir John Herschel 

 describes the intensity of solar radiation as nearly seven times 

 greater on Mercury than on the earth, and on Uranus 330 times 

 less ; the proportion between the two extremes being that of 

 upwards of 2000 to 1. Let any one figure to himself, (adds 

 Sir John,) the condition of our globe were the sun to be sep- 

 tupled, to say nothing of the greater ratio ; or were it dimi- 

 nished to a seventh, or to a 300th of its actual power ! 

 Again, the intensity of gravity, or its efficacy in counter- 

 acting muscular power and repressing animal activity, on Ju- 

 piter is nearly two-and-a-half times that on the earth ; on 

 Mars not more than one-half; on the moon one-sixth; and on 

 the smaller planets probably not more than one-twentieth ; 

 giving a scale of which the extremes are in the proportion of 

 sixty to one. Lastly, the density of Saturn hardly exceeds one- 

 eighth of the mean density of the earth, so that it must consist 

 of materials not much heavier than cork. 



Jupiter is eleven times, Saturn ten times, Uranus five times, and 

 Neptune nearly six times, the diameter of our earth. 



These four bodies revolve in space at such distances from the sun, 

 that if it were possible to start thence for each in succession, and to travel 

 at the railway speed of 33 miles per hour, the traveller would reach 



