366 



SCIEXCE. 



[Vol. VII, No. 168 



important but mysterious phenomenon, the zodia- 

 cal light. 



No inconsiderable number of persons sufficient- 

 ly interested in astronomy to read a book of 

 this sort desire to become themselves observers ; 

 not with reference to making contributions of 

 value to the science, but simply for their own ad- 

 vancement and edification. Early in his work, 

 Dr. Ball has an interesting word for such readers, 

 suggesting work well worth doing, and for which 

 only an opera-glass is required. Why not have 

 elaborated this idea more fully farther on, and 

 with reference to various celestial objects within 

 ready reach of slender telescopic means ? 



We are glad to see the care with which an 

 abounding index has been prepared : it contains 

 something like twelve hundred entries, and covers 

 no less than eleven pages of the book. 



In the last chapter, when treating of the tides, 

 Dr. Ball is at his best. And by tides are meant, 

 not alone the rise and fall of the sea as we note 

 it to-day, but the term is used in its broadest 

 sense, and the vast problems of tidal evolution 

 dealt with in a wholly captivating style. This 

 new departure in mathematical astronomy, as Dr. 

 Ball justly terms it, is fully elucidated, and the 

 non-mathematical reader owes him many an obli- 

 gation for this clear and elegant exposition of the 

 profound mathematical researches of Professor 

 Darwin. 



The illustrations are, as a whole, the best we 

 have seen in any book on popular astronomy. A 

 good many of them are new, a good many are 

 borrowed with full credit, and yet others are 

 borrowed without any credit. To the last class 

 belong a number appropriated from Newcomb's 

 ' Popular astronomy,' notably those on pp. 78 and 

 214 of the latter work, which are reproduced on 

 pp. 104 and 228 of Ball. Presumably the charge 

 of plagiarizing the text accompanying these illus- 

 trations would be sustained with difficulty ; but 

 it would be interesting to know how much time 

 elapsed between Dr. Ball's reading of this text, and 

 the writing of his own paragraphs on the effect 

 of gravity on a projectile, and on the toothed- 

 wheel method of determining the velocity of light. 

 In our way of looking at it, subtracting the 

 smoke from the lamp, and five teeth from the 

 wheel, and supplementing the man's head with 

 one shoulder and a mustache, fail to establish 

 one's right to an illustration otherwise success- 

 fully 4 conveyed.' 



But Dr. Ball has not confined his attentions to 

 a single work. In filling out his chapter on the 

 sun, lie found that something already written by 

 somebody else would save him the drudgery of a 

 page here and there, and he appears to have had 



no compunction in calling it his own. A few 

 paragraphs from Young's ' The sun ' and from 

 Ball's 1 The story of the heavens ' are subjoined : — 



YOUNG (p. 118). 



" The average life of a sun- 

 spot may be taken as two or 

 three months; the longest 

 yet on record is that of a 

 spot observed in 1840 and 

 1841, which lasted eighteen 

 months. . . . While some 

 spots are thus long-lived, 

 others. however, endure only 

 for a day or two, and some- 

 times only for a few hours. 



" The spots usually ap- 

 pear not singly, but in 

 groups — . . . Very often a 

 large spot is followed upon 

 the eastern side by a train 

 of smaller ones ; many of 

 which, in such a case, are 

 apt to be very imperfect in 

 structure, . . . When a large 

 spot divides into two or 

 more as often happens, the 

 parts usually seem to repel 

 each other, and fly asunder 

 . . . velocities of one thou- 

 sand miles, and even more, 

 are by no means exception- 

 al. 



"At times, though very 

 rarely, a different phenom- 

 enon of the most surprising 

 and startling character ap- 

 pears in connection with 

 these objects: patches of in- 

 tense brightness suddenly 

 break out, remaining visible 

 for a few minutes, moving, 

 while they last, with velo- 

 cities as great as one hun- 

 dred miles a second. 



" One of these events has 

 become classical. It oc- 

 curred on the forenoon 

 (Greenwich time) of Sept. 

 1, 1859, and was independ- 

 ently witnessed by two well- 

 known and reliable observ- 

 ers, Mr. Carrington and Mr. 

 Hodgson, . . . Mr. Carring- 

 ton at the time was making 

 his usual daily observation 

 upon the position, configu- 

 ration, and size of the spots 

 by means of an image of the 

 solar disk upon a screen, 

 . . . Mr. Hodgson, at a dis- 

 tance of many miles, was at 

 the same time sketching de- 

 tails of sun-spot structure 

 . . . They simultaneously 

 saw two luminous objects, 

 shaped something like two 

 new moons.each about eight 

 thousand miles in length 

 and two thousand wide, at 

 a distance of some twelve 

 thousand miles from each 

 other. These burst sudden- 

 ly into sight at the edge of 

 a great sun-spot, with a 



BALL (p. 36). 



The average duration of 

 a sun-spot is about two or 

 three months, and the lon- 

 gest life of a spot that has 

 been recorded is one which 

 in 1840 and 1841 lasted for 

 eighteen months. There are, 

 however, some spots which 

 last only for a day or two, 

 and some only for a few 

 hours. 



"It should also be ob- 

 served that the sun spots 

 usually appear in groups, 

 and very often a large spot 

 Is attended or followed by 

 a number of smaller ones, 

 more or less imperfect. It 

 often happens that a large 

 spot divides into two or 

 more smaller spots, and 

 these parts have been some- 

 times seen to fly apart, with 

 a velocity in some cases not 

 less than a thousand miles 

 an hour. On rare occasions 

 a phenomenon of the most 

 surprising character has 

 been witnessed in connec- 

 tion with the sun - spots, 

 where patches of intense 

 brightness suddenly break 

 out, remain visible for a 

 few minutes, and travel 

 with a velocity of over a 

 hundred miles a second. 

 One of these events has 

 become celebrated for 

 the extraordinary char- 

 acter of the phenomena, as 

 well as for the fortunate 

 circumstance that it has 

 been authenticated by the 

 independent testimony of 

 the skilled witnesses. On 

 the forenoon of the 1st Sep- 

 tember, 1859, two well- 

 known observers of the 

 sun, Mr. Carrington and Mr- 

 Hodgson, were both en- 

 gaged in observation. Mr. 

 Carrington was employed 

 at his self-imposed daily 

 task of observing the po- 

 sitions, the configuration, 

 and the size of the spots 

 by means of an image of 

 the sun upon a screen. Mr. 

 Hodgson, many miles away, 

 was at the same moment 

 sketching some details of 

 sun-spot structure. They 

 saw simultaneously two lu- 

 minous objects, shaped 

 something like two new 

 moons, each about eight 

 thousand miles long and 

 two thousand miles wide, 

 at a distance of about 

 twelve thousand miles 



