ON COMETS. 103 



to say that the velocity of light so concluded was found 

 to be somewhat less (and that by about one 3oth part) 

 of that which had been hitherto received (192,000 miles 

 per second) and which was concluded from the observed 

 fact of its traversing the diameter of the earth's orbit in 

 i6 m - 26 sec - of time, and very considerably less than that 

 before obtained by M. Fizeau, with a less perfect appa- 

 ratus, and a less delicate and refined system of procedure. 

 Now it will not fail to be remarked, that the time (16- 

 26 sec -) remaining unaltered, and the velocity diminished 

 by one 3oth, the distance traversed (the diameter of the 

 orbit) in that time will also be diminished by the same 

 aliquot fraction, so that there is a coincidence between 

 the two corrections of the sun's distance, which, coming 

 simultaneously, from such very different sources, cannot 

 but lead to their acceptance, at least provisionally, and 

 until the recurrence of that grand phenomenon, the 

 transit of Venus, which will take place in the year 1874, 

 shall put an end to all uncertainty on the subject of the 

 true numerical dimensions of our system. 



(10.) Bearing now these dimensions in mind, let us 

 construct in imagination a figure consisting of concentric 

 circles, to represent the orbits of the planets. Taking 

 the largest, that of Neptune, as 30 feet in diameter, then 

 will that of Uranus measure a little more than 19 feet 

 across, of Saturn somewhere less than 10, of Jupiter rather 

 more than 5, of Mars about 18 inches, and of the earth a 

 foot, while the enormous body of the sun will stand repre- 

 sented in the centre of all by a pellet of very little more 

 than one-ninth of an inch in diameter the orbits of 



