5*8 



THE POPULAR SCIENCE MONTHLY 



companion. That has seemed to me a 

 characteristic of such great men of 

 science as I have chanced to meet. 

 They are always face to face with the 

 transcendent mysteries of nature. . . . 

 Such labours produce a sublime calm, 

 and it was that which seemed always 

 to pervade Lord Kelvin. Surely in an 

 age fertile in distinction, but not lavish 

 of greatness, he was truly great." 



A PHOTOGRAPH OF HALLEY'S 



COMET 



Edmund Halley, born in 1656, 

 Savilian professor of geometry at Ox- 

 ford and later Flamsteed's successor as 

 astronomer royal, made notable contri- 

 butions to astronomy and cosmical 

 physics. He was the first to catalogue 

 the stars of the southern sky; he 

 studied the orbits of Jupiter and Sat- 

 urn; he detected the acceleration of 

 the moon's mean motion; he used the 

 transit of Venus to determine the solar 

 parallax; he discovered the proper mo- 

 tion of the fixed stars; he suggested 

 the magnetic origin of the aurora 

 borealis; he studied terrestrial mag- 

 netism and located magnetic poles; 

 he surveyed the tides and coasts of the 

 British Channel; he cooperated with 

 Newton in the publication of the 

 " Principia." 



But outside the circle of astron- 

 omers, Halley's name is known because 

 it is attached to a comet whose orbit 

 he calculated and whose return he pre- 

 dicted. This was in 1682, when Halley 

 computed its parabolic orbit, and com- 

 paring this with the imperfect observa- 

 tions of comets which had appeared in 

 1456, 1531 and 1607, concluded that 

 each was the same body returning 

 from the outer region of the solar sys- 

 tem beyond the furthest known planet. 

 He wrote : " Wherefore, if it should 

 return according to our predictions 

 about the year 1758, impartial pos- 

 terity will not refuse to acknowledge 

 that this was first discovered by an 

 Englishman." 



This was not only a great advance 

 in astronomy and important in its 



relation to the theory of gravitation, 

 but was a forward movement in the 

 conception of the orderliness of the 

 universe. Comets had been portents of 

 war, pestilence and famine. It was 

 indeed Halley's comet which appeared 

 in 1066 at the time of the invasion of 

 William the Conqueror and again in 

 1456 when Constantinople was besieged 

 by the Turks and the crescent- shaped 

 tail was a mighty omen. 



Halley's comet duly appeared 'in 

 1759, somewhat retarded by the attrac- 

 tion of Jupiter and Saturn, its per- 

 turbations having been accurately cal- 

 culated by the French astronomer, 

 Clairaut. It appeared again in 1835 

 and is now once more rapidly ap- 

 proaching the earth and the sun, hav- 

 ing passed the orbit of Jupiter in April 

 last. It has been observed by Pro- 

 fessor Max Wolf, of Heidelberg, and 

 we are able to give here photographs 

 taken by Mr. Oliver J. Lee with a two- 

 foot reflector at the Yerkes Observa- 

 tory. These are printed by the cour- 

 tesy of Dr. Edwin B. Frost, director 

 of the observatory and editor of the 

 Astrophysical Journal, where they are 

 also printed. 



The plate of September 16 was taken 

 with an exposure of 180 minutes, stan- 

 dard central time of mid-exposure 

 being 14 h 45 m (2:45 a.m. Sept. 17). 

 The comet's position, as measured on 

 the plate, was R.A. 6 h 18 m 56 s , Dec. 

 + 17° 9' 23". The plate of September 

 17 was exposed for 130 minutes, mid- 

 exposure at (central standard time) 

 14 h 10 m (2:10 a.m. Sept. 18). The 

 right ascension had increased by 4 s , 

 and the declination had decreased by 

 23". The arrows indicate the position, 

 and also the components of the direc- 

 tion of the comet's motion. 



The original negatives are magnified 

 about ten times, and the scale of the 

 pictures here is about 8". 5 to the milli- 

 meter, or 3.5 minutes of arc to the 

 inch; in other words, the width of 

 each picture is about one seventh of a 

 degree. The new Lumiere " Sigma " 

 plates were used, a fresh and clean 



