THE SMITHSONIAN INSTITUTION. 145 



would form planets in the state of vapor. If one of these masses were 

 large enough to attract each of the others in succession to itself, the 

 ring of vapor would be converted into a single spheroidal mass of vapor, 

 and we should have a single planet of great mass for each zone of 

 vapor detached. But if no one of these masses had a preponderating 

 size, they would all continue to revolve about the sun in independent 

 orbits, and would form a zone of little planets such as we have actually 

 discovered between Mars and Jupiter. 



With regard to the actual number of bodies belonging to this zone 

 of planets, we can do little more than hazard a plausible conjecture. 

 Already we have one asteroid of the sixth magnitude, one of the seventh, 

 four of the eighth, eighteen of the ninth, and nine of the tenth or 

 eleventh. It would require four hundred bodies as large as the largest 

 of the asteroids, to make a body one fourth of the size of the earth ; 

 and, according to Leverrier, the snm of all the asteroids cannot ex- 

 ceed this limit. When we consider the shortness of the period during 

 which stars below the eighth magnitude have been sj'Stematically ob- 

 served, we see room for the discovery of several more planets of the 

 ninth magnitude, and perhaps three or four hundred more of inferior 

 dimensions. 



With such a wonderful field of probable discovery inviting the 

 explorations of astronomers, maj' we not hope that the enterprize of 

 America will claim its share of the labor of this research? The rapid 

 progress which the last few years have witnessed in our country, both 

 in the facilities for observation, and in the number of active observers, 

 is one of the most encouraging signs of the times. It is scarcely a 

 quarter of a century since the first telescope, exceeding those of a 

 portable size, was imported into the United States ; and the introduction 

 of meridional instruments of the laro;e class is of still more recent date. 

 Now we have one telescope which acknowledges no superior ; and we 

 have several which would be esteemed worthy of a place in the finest 

 observatories of Europe. We have also numerous meridional instru- 

 ments of dimensions adequate to be employed in original research. 

 These instruments have not been permitted to remain unemployed. 

 At the Observatory in this city, and also at Cambridge, extensive cata- 

 logues of stars are now in progress ; while neai'ly ever}- known mem- 

 ber of our solar system has been repeatedly and carefully observed. 

 These observations are all permanently recorded by a simple touch of 

 the finger upon a key which closes an electric circuit — a method re- 

 centh" introduced at Greenwich Observatory, and known everywhere 

 throughout Europe by the distinctive name of the American method. 



Numerous, important, and striking discoveries have been the result 

 of this astronomical activity. A host of comets have been indepen- 

 dently discovered on this side of the Atlantic ; and among them three, 

 at least, were observed here before they were seen in Europe. The 

 two nebulce which have been longest and best known, and which 

 have attracted the wonderina; o;aze ofeverv astronomer since the inven- 

 tion of the telescope, were never adequately figured until an Anjerican 

 eye saw them, and an American pencil depicted them. The planet 

 Saturn, which, for many years, was made the subject of special study 

 by the elder Herschel, with his wonderful means of observation, first 

 Mis. Doc. 24 10 



