392 THE POPULAR SCIENCE MONTHLY. 



Verrier, and other observers. He not only shows that the orbits of 

 meteors are quite coincident with those of comets, and that the same 

 object may appear to us at one time as a comet, and at another as a 

 shower of meteors, but he proves also by a highly-elegant mathemati- 

 cal calculation that the scattered cosmical masses known to us by the 

 name of nebula would, if in their journey through the universe they 

 were to come within the powerful attraction of our sun, be formed into 

 comets, and these again into meteoric showers. 



We should be carried away too far from our subject were we to 

 enter fully into the consideration of this bold and ingenious theory of 

 the Milan astronomer, supported though it be by a series of facts ; but 

 while we refer the reader to vol. xx. of " Naturwissenschaftlichen 

 Volksbticher," by A. Bernstein, in which this subject, " die Rathsel 

 der Sternschnuppen und der Kometen." is fully treated of in a very 

 clear and attractive manner, we shall confine ourselves to the following 

 short statement of Schiaparelli's theory : 



Nebulae are composed of cosmical matter in which as yet there is 

 no central point of concentration, and which has not become sufficiently 

 dense to form a celestial body in the ordinary sense of the term. The 

 diffuse substance of these cosmical clouds is very loosely hung to- 

 gether ; its particles are widely separated, thus constituting masses of 

 enormous extent, some of which have taken a regular form, and some 

 not. As these nebulous clouds may be supposed to have, like our sun, 

 a motion in space, it will sometimes happen that such a cloud comes 

 within reach of the power of attraction of our sun. The attraction 

 acts more powerfully on the preceding part of the nebulae than on the 

 farther and following portion ; and the nebula, while still at a great 

 distance, begins to lose its original spherical form, and becomes con- 

 siderably elongated. Other portions of the nebulous mass follow con- 

 tinuously the preceding part, until the sphere is converted into a long 

 cylinder, the foremost part of which, that toward the sun, is denser 

 and more pointed than the following part, which retains a portion of 

 its original breadth. As it nears the sun, this transformation of the 

 nebulous cloud becomes more complete : illuminated by the sun, the 

 preceding part appears . to us as a dense nucleus, and the following 

 part, turned away from the sun, as a long tail, curved in consequence 

 of the lateral motion preserved by the nebula during its progress. Out 

 of the original spherical nebula, quite unconnected with our solar sys- 

 tem, a comet has been formed, which in its altered condition will either 

 pass through our system to wander again in space, or else remain as a 

 permanent member of our planetary system. The form of the orbit in 

 which it moves depends on the original speed of the cloud, its distance 

 from the sun, and the direction of its motion, and thus its path may be 

 elliptical, hyperbolical, or parabolical ; in the last two cases, the comet 

 appears only once in our system, and then returns to wander in the 

 realms of space ; in the former case, it abides with us, and accomplishes 



