152 Scientific Intelligence. 



present work is much on the same plan as Page's book with the 

 statistics and distribution of American products made more com- 

 plete and prominent ; and the author has added several excellent 

 chapters on structural geology and physical geography which 

 removes the book from being an aggregate of statistics regarding 

 valuable geological products. w. 



III. ASTKONOMY AND SEISMOLOGY. 



1. The force that acts on the meteoroids after they have left the 

 comets. — (Communication by H. A. Newton to the American 

 Philosophical Society at its recent sesquicentennial.) 



There are in the comets so many questions that we cannot 

 answer, so many curious and wonderful phenomena that are un- 

 explained, that I am sure you will accept any explanation of any 

 of them that seems plausible, as a matter of interest. From a 

 comet there is continually driven off matter forming the tail, a 

 light substance, and astronomers are agreed that the force that 

 acts on the matter which forms the tail is a repulsive force from 

 the sun acting inversely as the square of the distance, the force 

 of the repulsion being greater than that of attraction. 



Not only is this true, but different parts of that tail are acted 

 upon by repulsive forces of different powers; otherwise the tail 

 would form across the sky a single line instead of a broad, ex- 

 panded mass of light such as we see. From the comet, however, 

 there are driven off also, or there are separated other things 

 entirely distinct from the tail, small bodies, which are not thus 

 driven away, which are not visible, but follow along closely in 

 the path of the comet, and whenever the occasion comes, that is 

 when we go through a group of them, those give us our shooting 

 stars. 



The Biela comet, in the period about 1840, passed near to 

 Jupiter. At that time it was turned pretty sharply out of its 

 orbit, the inclination of the orbit being turned several degrees, 

 and the node being carried forward also several degrees, repre- 

 sented by several days in the time at which we crossed the path 

 of the comet. 



After 1840 the bodies which formed the meteors that were met 

 in 1872 and in 1885 were separated from one or other parts of 

 the Biela comet. I say after 1840, because if they had been 

 separated earlier they would have given us a different radiant in 

 the skies, the one given by the Biela meteors of 1838. The 

 radiant was changed, the node was changed, all to correspond to 

 the new orbit, and these bodies could not have been turned in 

 that way had they been before scattered, because the force that 

 acted on them, the attraction of Jupiter, would have scattered 

 the group instead of giving us that single compact group through 

 which we passed in 1872 and 1885 in the course of four or five 

 hours, and the bulk of them even in two hours. 



