March 27, 1908] 



SCIENCE 



513 



after his death. Pontecoulant was one of at 

 least five mathematicians who computed the 

 last return of Halley's comet in 1835. It 

 reached perihelion within a few days of the 

 predicted time. Pontecoulant also made the 

 necessary computations for the next return, 

 and published his results in 1864. His date 

 for perihelion is May 24, 1910. It was to be 

 expected that before the time for its return 

 various astronomers would be sufficiently in- 

 terested in the problem to redetermine the 

 elements. So far this appears to have been 

 undertaken only by the English astronomers, 

 Cowell and Crommelin. It is interesting to 

 know that the results which they obtain are 

 in substantial agreement with those of Ponte- 

 coulant, so that the comet may be confidently 

 expected to reach perihelion passage in May, 

 1910. Astronomers will not wait till that 

 time, however, for their first view of the comet. 

 Professor O. C. Wendell has published in the 

 February number of Popular Astronomy an 

 ephemeris based on the elements of Ponte- 

 coulant. From this it appears that at the 

 present time the comet is less distant from 

 the sun than Saturn. Its position, in the 

 northern edge of the constellation Orion, is 

 favorable for observation, but it is doubtful 

 if even the great telescopes of the present day 

 can reach it at present. Owing to the form 

 of its orbit and its distance, the comet is 

 moving in nearly a direct line toward the sun, 

 and as viewed from that luminary would ap- 

 pear to stand nearly stationary in the sky. 

 Owing to the motion of the earth, however, it 

 will sway, during the next year and a half, 

 backward and forward on the borders of Orion, 

 Monoceros, Gemini and Taurus. About the 

 first of October, 1909, its apparent motion will 

 become very rapid as it approaches the sun. 

 After April of the present year it will be un- 

 favorably placed for several months. Next 

 year the conditions will be somewhat similar, 

 except that by January, 1909, the distance of 

 the comet from the earth will be only that of 

 the orbit of Jupiter. By October, 1909, the 

 distance will have decreased to about 300 mil- 

 lions of miles, and by that time, if not before, 

 the comet will probably have been " picked 

 up " photographically or visually. 



The mean period of Halley's comet is 76 

 or 77 years, but, owing to the powerful per- 

 turbations of the gTeat planets, this period 

 varies much. Cowell and Crommelin state 

 that the revolution of 1222 to 1301 was the 

 longest on record, taking 79 years and 2 

 months, while the present round is the short- 

 est, only 74 years and 5.5 months. It is be- 

 lieved that apparitions of this comet have been 

 recorded during the last 2,000 years, but the 

 identity of the earliest appearances has not 

 yet been certainly established. 



S. I. Bailey 



Harvard Coluege Observatory 



BOTANICAL NOTES 

 TREES AND LIGHTNING 



In the " Notes from the Eoyal Botanic 

 Garden of Edinburgh" (No. XIV.) Dr. A. 

 W. Borthwick discusses some of the effects of 

 lightning strokes upon various kinds of trees. 

 He begins by referring to the "widespread 

 popular belief that certain trees are less liable 

 than others to be struck by lightning, and 

 that during a thunderstorm it is quite safe 

 to stand under a beech for example, while 

 the danger under a resinous tree or an oak is 

 respectively fifteen or fifty times greater." 

 This and other questions, as of the exact 

 nature of the injury done to the tissue of the 

 tree, the author takes up and examines with 

 care. He concludes with reference to the 

 first point " that no tree is immune " since 

 " lightning will select one species quite as 

 readily as another," and " that the beech is 

 struck quite as frequently as any other 

 species." Apparently the taller trees in a 

 neighborhood are the ones most liable to be 

 struck. Contrary to what is believed by some 

 people the cells are not " ruptured or torn by 

 the formation of steam, as might happen if 

 the heating by the electric current was very 

 great. The cells collapse and shrink up, but 

 are never torn." The root system does not 

 seem to be ever damaged by lightning. 



as to birdseye maple 

 Many a botanist has puzzled over the ques- 

 tion of the nature and cause of the peculiar 



