60 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



date previous to 1772 at which they could have been in close 

 proximity; and Kirkwood considers it probable that the 

 members of this cometary cluster were at that time throAvn 

 into their present elliptical orbit, and that since then the 

 various members of the group, by collisions with each other, 

 and possibly with meteoric streams, have become gradually 

 separated. By assigning this as the date at which Biela's 

 comet entered the solar system, Kirkwood explains the fact 

 that the meteors, which have been five times observed since 

 1798, are not recorded to have been observed previous to 

 that date, whereas other systems of meteors connected with 

 other cometary groups may be traced back many centuries. 

 6i>, 1873, 21. 



THE DAILY PHOTOGRAPHS OF THE SUN. 



Professor Winlock, of Cambridge Observatory, states that 

 by the last year's work he has been able to secure photo- 

 graphs of the sun on at least twenty-five days in each month 

 on the average, beiog far more successful than the astrono- 

 mers of London, who have reported an average of eighteen 

 monthly. This striking difiTerence is due to the atmospheric 

 peculiarities of the two cities though doubtless something 

 is to be argued in favor of the extremely simple apparatus 

 used at the Harvard College Observatory. Professor Win- 

 lock estimates that if a similar work were to be undertaken 

 in Washington, there would result, by combining the two 

 series of photographs, a perfect daily series, without any gaps, 

 and one that would contribute much to our knowledsje of the 

 cycle of solar- spot changes, which is believed to exert so 

 decided an influence over meteorological phenomena. 



FAINT VARIABLE STARS AND ASTEROIDS. 



Professor Watson, of Ann Arbor, announces as the result 

 of many years' careful study of the faintest visible stars, in 

 his search for new asteroids, the following important conclu- 

 sions: 1. The asteroids are not generally to be classed among 

 the faintest telescopic objects, but are much brighter than 

 the faint stars among which they move. 2. The number of 

 asteroids is probably not imlimited, but, on the contrary, 

 comparatively very restricted, and very possibly does not ex- 



